강상관계 물리

• Title: Chiral Light Meets Chiral Quantum Materials

• Speaker: Prof. Junyeong Ahn (The University of Texas at Austin)

• Date & Time / Venue: August 11th (Mon.), 2025, 3:30 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Chirality, the lack of mirror symmetries in odd space or spacetime dimensions, is a fundamental concept with profound consequences in chemistry, biology, and physics. In condensed matter systems, chirality enables exotic phenomena that are otherwise forbidden by the high symmetry of crystalline lattices. This seminar explores how chiral quantum materials interact with chiral light, a frontier topic that brings together symmetry, topology, and light-matter interaction in intriguing ways. I will present recent theoretical developments across three material platforms: topological semimetals, magnetic materials, and unconventional superconductors. These examples reveal how broken symmetries enable new optical phenomena, offering insights relevant for both fundamental science and potential applications in quantum technologies.

• Title: Quantum Entanglement in Solids: A Case Study on Pyrochlore Iridates

• Speaker: Prof. Kwon Junyoung (POSTECH)

• Date & Time / Venue: July 25th (Fri.), 2025, 2:00 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : 최근 전자 통신 기술의 혁신의 일환으로 양자 통신 및 양자 컴퓨팅 기술에 대한 관심이 급속히 증가하고 있습니다. 이에 따라 소재공학적 기술과 양자역학적 기초 과학 간의 긴밀한 연계가 중요한 연구 방향으로 대두되고 있습니다. 본 연구는 양자 정보 기술의 가장 근본적인 개념인 양자 얽힘 현상이 고체 물질 내에서 어떻게 구체적으로 나타날 수 있는지에 대해 고찰한 결과입니다. 광학 및 나노 시스템과 달리, 고체 내 양자 얽힘은 다체 상호작용과 전자 간의 강한 상관성으로 인해 분석이 매우 도전적인 과제로 여겨져 왔습니다. 본 연구에서는 결정 구조적 및 전자 구조적으로 강한 양자 섭동 특성을 지닌 이리듐 기반 파이로클로르 시스템을 타겟으로 하여, 다전자 파동함수가 공간군 대칭성 하에서 양자적으로 얽힌 상태로 존재할 수 있음을 이론적으로 도출하였습니다. 특히 이러한 얽힘은 고차원 자기 정렬 상태의 형성으로 이어질 수 있음을 제안합니다. 이를 위해 본 연구에서는 고품질의 Nd₂Ir₂O₇ 단결정을 자체적으로 성장하였으며, 공명 비탄성 X선 산란 기법을 이용하여 양자적으로 얽힌 국소 전자들의 파동 함수 형태에 따른 실공간 상에서의 간섭 패턴을 관측하였습니다. 이를 기반으로 완전 대각화 계산을 수행하여, 실제 양자 얽힘이 반영된 전자 파동함수를 유도하였고, 이를 통해 기존에 보고된 단순한 반강자성 정렬 외에도 고차원 자기 모멘트 정렬이 공존 가능함을 확인하였습니다. 향후 본 연구단은 해당 결과를 기반으로 양자 얽힘 현상을 보다 강하게 구현할 수 있는 새로운 양자 물질 설계 및 합성을 지속적으로 추진할 계획이며, RIXS 및 다른 X선 분광 실험 기법들을 이용하여 양자 얽힘 상태의 실험적 탐색을 확장해 나갈 예정입니다. 이러한 연구는 양자 얽힘을 활용한 차세대 양자 소재 개발에 있어 선도적인 역할을 수행할 수 있을 것으로 기대됩니다.

• Title: Antiferromagnetic quantum critical metal and Kondo effect

• Speaker: Prof. Sung-Sik Lee (McMaster University & Perimeter Institute)

• Date & Time / Venue: June 26th (Thu.), 2025, 3:00 PM / APCTP (HogilKim Memorial Bldg., #512)

• Abstract
  : We study a magnetic impurity immersed in the two-dimensional antiferromagnetic quantum critical metal. Critical spin fluctuations represented by a bosonic field compete with itinerant electrons to couple with the impurity through the spin-spin interaction. At long distances, the antiferromagnetic electron-impurity (Kondo) coupling dominates over the boson-impurity coupling. However, the Kondo screening is weakened by the boson with an increasing severity as the hot spots connected by the magnetic ordering wave-vector are better nested. The remarkable efficiency of the single collective field in hampering the screening of the impurity spin by the Fermi surface originates from a ultraviolet/infrared (UV/IR) mixing where critical spin fluctuations of all length scales actively suppress Kondo screening at low energies.

• Title: Growth and characterization of oxide freestanding membranes for future stacktronics in TEM

• Speaker: Prof. Celesta Soyeon Chang (Dept. of Physics and Astronomy, Seoul National University)

• Date & Time / Venue: May 29th (Thu.), 2025, 3:30 PM / Science Bldg Ⅲ, #111

• Abstract
  : Recent growth of research on freestanding oxide membranes are now heading towards stacktronics and twistronics, in the hopes of achieving unprecedented physical couplings. Unlike 2D materials that can easily be grown as single-crystalline and transferred by their weak vdW force in between layers, high quality oxide freestanding membranes are much more difficult to achieve. In this talk, we will mention several epitaxial methods for obtaining oxide membranes combined with TEM characterization to show the underlying principles of each method. Remote epitaxy, van der Waals epitaxy, and pinhole epitaxy will be discussed. Moreover, a ground-breaking method called atomic lift-off (ALO) method will be introduced that can be used for fabricating room temperature far-IR sensors. In the second part of the talk, we will briefly discuss multislice electron ptychography (MEP) that reconstructs the phase information of the object function, that enables a resolution of 23 picometers. With MEP, we provide an outlook for stacktronics/twistronics in the TEM field.

• Title: Short-range order in a two-dimensional dipole liquid

• Speaker: Prof. Keun Su Kim (Yonsei Univ.)

• Date & Time / Venue: May 21st (Wed.), 2025, 4:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Many fascinating quantum phenomena, such as high-temperature superconductivity, were found in a two-dimensional (layered) insulator doped by foreign dopants. Although these dopants have been often neglected in theoretical models for the sake of brevity, it is true that they remain in actual materials. More importantly, these dopants seem to be arbitrarily distributed at first glance, but they may form a short-range order characterized by broad peaks in the structure factor arising from an average distance between dopants. In this talk, I will introduce some of our recent works using angle-resolved photoemission spectroscopy (ARPES) on the effect of this short-range order to the electronic structure. The material system is a two-dimensional layered insulator (black phosphorus) doped by alkali metals. It could be modeled by a system of two-dimensional dipoles that consist of doped electrons and dopant ions. We found the short-range order is responsible for the pseudogap1 and the anomalously aperiodic dispersion (electronic roton)2. If time permits, I will also discuss on the dark state of electrons in a system with two pairs of sublattices3, and the direct measurement of a full quantum metric tensor in black phosphorus4.
  
  References
  S. H. Ryu et al., Nature 596, 68 (2021).
  S. Park et al., Nature 634, 813 (2024).
  Y. Chung et al., Nature Phys. 20, 1582 (2024).
  S. Kim et al., accepted in Science (2025).

• Title: Tailoring oxygen in complex oxides for novel materials

• Speaker: Prof. Woo Jin Kim (Pusan National University)

• Date & Time / Venue: May 22nd (Thu.), 2025, 4:00 PM / Room 104, IBS POSTECH Campus Building

• Abstract
  : Due to their multiple oxidation states, transition metal oxides can exist in various forms with different structure symmetries. By selectively introducing or removing oxygen from specific sites in a crystal lattice, it is possible to manipulate the material's electronic structure, leading to the emergence of quantum phenomena, such as colossal magnetoresistance and superconductivity [1,2]. Topotactic redox reactions allow for this reversible reduction and oxidation process to occur without altering the relative structure of the cations of the material. In this talk, I will discuss a quasi-two-dimensional material system that is stabilized through topotactic reduction, where the Jahn-Teller effect results in a beautiful pattern of distortions [3]. In the second half of the talk, I will introduce the use of mechanochemistry on freestanding oxide membranes to greatly reduce energy activation for redox reactions, which can be useful for creating new and clean functional oxides.
  
  [1] R. von Helmolt et al., Phys. Rev. Lett. 71, 2331–2333 (1993).
  [2] D. Li et al., Nature 572, 624–627 (2019).
  [3] W. J. Kim et al., Nature 615, 237-243 (2023).

• Title: Unusual ferromagnetic band evolution in monolayer 1T-CrTe₂ on bilayer graphene

• Speaker: Prof. Jinwoong Hwang (Kangwon National University)

• Date & Time / Venue: May 8th (Thu.), 2025, 4:00 PM / Room 104, IBS POSTECH Campus Building

• Abstract
  : Two-dimensional (2D) layered ferromagnetic materials have attracted much interest recently since the discovery of intrinsic 2D ferromagnetism (FM) in atomically thin layers. However, the evidence of 2D ferromagnetic transitions in viewpoint of band structures are still missing due to the difficulty of the sample preparation. In this talk, I will introduce a recent study on a monolayer (ML) 1T-CrTe₂ grown on bilayer graphene substrate. The combining study of molecular beam epitaxial (MBE) growth and in-situ angle-resolved photoemission spectroscopy (ARPES) characterization found exotic temperature-dependent band evolutions with FM transition in ML 1TCrTe₂, and we will discuss the mechanism of the FM transition in ML 1T-CrTe₂.

• Title: Emergent Charge-density-wave Phases Investigated with Ultrafast Optical Spectroscopy

• Speaker: Prof. Soyeun Kim (DGIST)

• Date & Time / Venue: Apirl 16th (Wed.), 2025, 4:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : One of the key objectives of condensed matter physics is to understand novel phase transition mechanisms where various degrees of freedom are strongly coupled. Investigating quasiparticles intrinsic to these phases is crucial for diagnosing the underlying emergent phases and their associated physics. Optical spectroscopy encompasses a wide range of experimental techniques that provide vital physical observables, including optical conductivity, dielectric constants, optical transitions, and quasiparticle energies [1].
  The capabilities of optical spectroscopy have been significantly enhanced by recent advances in femtosecond lasers and free-electron lasers, enabling the study of nonlinear regimes and lattice dynamics. These advancements reveal detailed physical properties of materials and the interplay between charge, spin, lattice, and orbital degrees of freedom, often leading to the discovery of emergent phase transitions [1,2].
  This seminar will provide an overview of various spectroscopic techniques and their applications, with a particular focus on the quasi-one-dimensional charge-density-wave (CDW) phase in a two-dimensional lattice of TbTe₃ and GdTe3 under external uniaxial strain. We will estimate the phenomenological free energy potential of the CDW phase by monitoring the associated order parameters [3]. Using femtosecond light pulses, our approach enables the detection of elusive collective modes that were previously inaccessible, demonstrating the essential role of ultrafast spectroscopy in unraveling complex electronic and lattice structures in quantum materials.
  
  [1] S. Kim, M.C. Lee et al., Adv. Mater. 30, 1704777 (2018).
  [2] S. Kim et al., Nat. Mater. 22, 429 (2023).
  [3] S. Kim et al., Rep. Prog. Phys. 87, 100501 (2024).

• Title: Exotic quantum phases in quasiperiodic systems

• Speaker: Prof. Sungbin Lee (KAIST)

• Date & Time / Venue: April 10th (Thu.), 2025, 4:00 PM / Room 104, IBS POSTECH Campus Building

• Abstract
  : Quasiperiodic systems offer a unique platform for realizing exotic quantum phases that challenge conventional understanding of condensed matter phenomena. In this work, we explore the emergence of long-distance magnetic correlations and pattern-selective superconductivity in quasiperiodic systems. By tuning quasiperiodicity parameters and interaction strengths, we identify regimes where magnetic order develops over unexpectedly long ranges in the absence of translational symmetry. Furthermore, we demonstrate that superconducting pairing in these systems can exhibit strong spatial selectivity, favoring distinct local configurations — an effect rooted in the underlying aperiodic geometry. These findings shed light on the interplay between structural complexity and collective quantum behavior, opening new avenues for designing materials with unconventional magnetic and superconducting properties.

• Title: Charge density waves in quantum materials

• Speaker: Prof. Yeongkwan Kim (KAIST)

• Date & Time / Venue: April 3rd (Thu.), 2025, 4:00 PM / Room 104, IBS POSTECH Campus Building

• Abstract
  :The charge density wave (CDW), the ununiform distribution of itinerant charge density, has been found and studied in various low-dimensional systems for decades. Despite extensive investigations, the many characteristics of CDW remain unknown; a microscopic mechanism other than the Pierls instability is required, and how CDW intertwines with other competing phases, particularly with the superconductivity, should be investigated. Furthermore, the recent compelling evidence has cast light on the unexpected aspect of CDW, additional symmetry breakings that accompany or occur concurrently with the CDW transition.
  In this talk, I will discuss various aspects of CDWs in different quantum materials, i) the additional symmetry breaking in CDW phase of 1T-TiSe2 and CsV3Sb5 systems, which are footprinted in the intensity of angle-resolved photoemission spectroscopy, ii) the possible role of CDW fluctuation on Cooper pairing, which is accomplished by analyzing the low-energy electronic structure of 2H-TaSe2.

• Title: Electronic structure studies of altermagnetism

• Speaker: Prof. Changyoung Kim (Seoul National University)

• Date & Time / Venue: March 26th (Wed.), 2025, 4:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : The third class of magnetism, dubbed as altermagnetism, has been a recent hot topic in the field of magnetism. Altermagnets have characteristics of both ferro- (FM) and antiferro-magnetism (AFM): spin split bands (thus broken time reversal symmetry) and zero net magnetization. These traits may be important in the fundamental scientific point of view as well as for spintronic applications.
  In this colloquium talk, I first wish to introduce the concept of altermagnetism. I will first talk about ABCs of altermagnetism – collinear AFM (zero net magnetization) and spin split bands (time reversal symmetry breaking) in terms of symmetries. Then, I will discuss the microscopic origin of the spin splitting based on the AFM order and structural distortion.
  Experimental verification of altermagetism is inherently difficult due to the zero net magnetization as well as domain formation. Yet, evidences for spin split bands can be obtained in some cases. I will introduce our recent ARPES work on an altermagnet MnTe. ARPES data show split bands which merges to a single band above the Neel temperature, strongly indicating the magnetic origin of the splitting. Finally, I will also briefly introduce recent study results on magnetic responses of RuO2 and domain switching behavior in MnTe/Bi2Te3 hetero structures.
  
  

• Title: Artificial Construction of Magnetic Atomic Structures on a Superconductor

• Speaker: Dr. Howon Kim (IBS Center for Quantum Conversion Research)

• Date & Time / Venue: March 12th (Wed.), 2025, 4:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : The interplay between magnetism and superconductivity in low-dimensional systems has attracted significant attention due to its fundamental importance in condensed matter physics and potential applications in quantum computation. These hybrid systems serve as a platform for exploring exotic quantum phenomena, such as unconventional superconducting phases and quasiparticle bound states. In this work, we employ atomic manipulation techniques to construct precisely-engineered magnetic atomic structures on superconducting surfaces. This bottom-up approach enables the creation of model low-dimensional magnetic systems with atomic precision, offering unprecedented control over their geometry and properties.
  Using scanning tunneling microscopy and spectroscopy (STM/STS), we investigate the local electronic and magnetic properties of these artificial structures. Our primary focus is on the emergence of exotic low-energy quasiparticle bound states, stemming from the conventional quasiparticle bound states such as Yu-Shiba-Rusinov states, which result from the interaction between magnetic moments and the superconducting condensate. By engineering magnetic structures atom-by-atom, we systematically study the spatial distribution, energy spectra, and behavior of these bound states as a function of the geometry and magnetic configuration of the system. This includes exploring the effects of different magnetic ground states, such as ferromagnetic, antiferromagnetic, and non-collinear arrangements.
  Our approach provides new insights into the mechanisms underlying the magnetism-superconductivity interplay in low-dimensional systems. The ability to precisely control and probe these hybrid systems at the atomic scale opens new avenues for designing atomic-scale quantum devices. These findings advance the understanding of magnetic-superconductor hybrids and their potential applications in quantum information technologies, including topological superconductors and Majorana-based quantum computing platforms.
  
  

• Title: The Past, Present, and Possible Future of Condensed Matter Theory

• Speaker: Prof. Eun-Gook Moon (KAIST)

• Date & Time / Venue: March 5th (Wed.), 2025, 4:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Condensed matter theory has significantly advanced our understanding of physical systems, from fundamental principles to technological innovations. This talk will explore its historical foundations, current research frontiers, and future directions. Key topics include high temperature superconductors, fractional quantum Hall, and emergent phenomena in strongly correlated systems. We will also discuss recent advances in computational methods and machine learning applications. Looking forward, we will consider the potential impact of condensed matter theory on quantum science and technology, novel materials design, and interdisciplinary fields. By reflecting on its past, present, and future, this colloquium aims to highlight the field’s enduring significance and future prospects.

• Title: Electron-phonon interactions and dynamics from first-principles

• Speaker: Prof. Jinsoo Park (POSTECH)

• Date & Time / Venue: February 19th (Wed.), 2025, 4:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : When electrons move in a crystal, they interact with lattice vibrations arising from the thermal motion of the atoms?i.e., phonons. This electron-phonon (e-ph) interaction is pervasive in condensed matter, governing phenomena such as charge transport, spin dynamics, and superconductivity. However, e-ph interaction is challenging to predict from a theoretical perspective, as the coupling depends rapidly on the band and momentum of both electrons and phonons. In this talk, I will introduce a first-principles framework for e-ph interaction using localized orbitals, which has become a gold standard for studying e-ph interactions and related physics in a wide range of quantum materials. I will discuss strategies for addressing polar and nonpolar materials, weak to moderate electron correlation, and both spin-collinear and noncollinear magnetism. These advancements uniquely position us to study electron motion in a diverse class of systems, ranging from silicon for conventional semiconductor technology to spin qubits embedded in diamond for quantum information science. Our efforts are implemented in Perturbo, an open-source software package for first-principles electron interactions, charge transport, and ultrafast carrier dynamics.

• Title: Quantum Resistive Switching through Disorder and Correlation

• Speaker: Prof. Jong Eun Han (Department of Physics, State University of New York at Buffalo)

• Date & Time / Venue: January 16th (Thu.), 2025, 12:00 PM /  APCTP (HogilKim Memorial Bldg., #501)

• Abstract
  : Insulator-to-metal transition under an electric field, known as resistive switching, remains unresolved. The diverse nature of this nonequilibrium transition has defied a reliable theoretical description even at the most basic level, whether the transition is of thermal or quantum nature. In this informal talk, I will present preliminary results where we considered the interplay of disorder, a key ingredient in the subject, with the electron correlation. We model the disorder by the coherent potential approximation (CPA) within the DMFT scheme. The disorder strongly affects the low energy correlated states, and even a weak disorder drastically changes the ingap spectrum into the so-called V-shaped DOS. This disorder-induced ingap physics on the single-band Hubbard model, which has been considered an unlikely model for resistive switching, supports an insulator-to-metal transition (IMT) with a strongly discontinuous transition at electric field much smaller than the crossover IMT fields without the disorder. The ingap states mediate strong nonequilibrium charge excitations across the Mott gap, sometimes as strong as to induce a population inversion between the Mott bands. We also investigate the pitfalls of perturbation approximations.
  This model presents an IMT mechanism without a thermal transition. The dependence of the IMT with the temperature and dephasing rate suggests quantum mechanical origin. The nonequilibrium metallic state after the IMT has an extremely long decay time back to the insulating ground state and persists as a supercooled metal at zero field and zero temperature. We will discuss this many-body and disorder-driven non-volatile metal (presumably a doublon-holon liquid) and its possible experimental implications. 

• Title: Dzyaloshinskii-Moriya interaction and exotic spin structures

• Speaker: Dr. Oleg Utesov (IBS)

• Date & Time / Venue: January 16th (Thu.), 2025, 12:00 PM /  APCTP (HogilKim Memorial Bldg., #501)

• Abstract
  : Although many years passed since the Dzyaloshinskii-Moriya interaction (DMI) was introduced to the field of magnetism of condensed matter systems, corresponding compounds are still the subject of intensive studies. Contemporary topics include research on their complex phase diagrams, creation, and manipulation of various solitonic-like objects, the interplay between electronic and magnetic degrees of freedom, topological properties, etc. There are also several perspective applications, for instance, the creation of nanometer-size inductors with chiral magnetic structures, stochastic information processing with skyrmions, and magnetic racetrack memory. In the present talk, I will review crucial for understanding the physics of DMI magnets theoretical concepts. We will discuss typical magnetic phase diagrams and properties of the corresponding phases, skyrmions, and topological Hall effect physics. Finally, I will present an overview of the state-of-the-art experimental techniques for investigating the DMI helimagnets' intriguing properties.

• Title: Time-resolved x-ray scattering study on polar vortex structures using XFEL

• Speaker: Dr. Kooktae Kim (POSTECH)

• Date & Time / Venue: January 20th (Mon.), 2025, 4:00 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Ferroelectric topological structures, such as polar vortices and skyrmions in SrTiO3/PbTiO3 heterostructures, have garnered significant attention due to their unique physical properties, including controllable emergent chirality, sub-terahertz collective dynamics, and negative capacitance. These structures are characterized by very small domain sizes, on the order of 10 nm, and are anticipated to exhibit nanoscale piezoelectric properties not previously observed, owing to their continuous rotation of electric polarization vectors with periodic lateral arrangement. In this study, to study piezoelectric response of polar vortex, we generated coherent acoustic phonons (CAPs) propagating at the speed of sound within a sample using an 800 nm optical pump laser and a metallic transducer, and observed the interaction between the CAPs and the polar vortex in real time via time-resolved resonant elastic x-ray scattering (TR-REXS) and time-resolved x-ray diffraction (TR-XRD). By employing these two distinct techniques, we were able to observe two different types of order parameters—polarization vector and strain—independently, which allowed us to track the alterations in the polar vortex structure induced by the ultra-fast strain wave, as well as the changes in the CAP as it exited the polar vortex. Upon analyzing the experimental data, we found that the rotation direction of polarization vectors oriented diagonally within the vortex can be opposite depending on the strain wave’s sign. We also demonstrated that CAPs interacting with the vortex may exhibit a non-uniform wavefront due to CAP scattering by the non-uniform piezoelectric coefficient along the periodic structure of the polar vortex. Given that ferroelectric topological structures can be easily deformed by external stimuli such as pressure, temperature, and electric fields, our findings are expected to have significant implications for future applications, particularly in fields such as phonon engineering that utilize polar topological structures.

• Title: Electric field control of superconductivity and quantized anomalous Hall effects in rhombohedral tetralayer graphene

• Speaker: Dr. Youngjoon Choi (University of California Santa Barbara)

• Date & Time / Venue: January 9th (Thu.), 2025, 4:00 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Inducing superconducting correlations in chiral edge states is predicted to generate topologically protected modes with exotic quantum statistics. Past experimental efforts have focused on engineering interfaces between superconducting materials and quantum Hall systems. We present rhombohedral tetralayer graphene as an ideal platform for these hybrid interfaces leveraging the gate-tuned ground states between intrinsic superconductors and quantum anomalous Hall states. We find multiple superconducting states, including one phase with critical temperature Tc = 55mK at superlattice filling ν≈ −3.5 for layer polarization corresponding to a weak moire potential. Quantized anomalous Hall effect occurs at ν = −1 for weak moire potential, with a measured Chern number |C| = 4. Remarkably, gate voltage can also trigger nonvolatile switching of chirality in the quantum anomalous Hall state, enabling reconfiguration of topological edge mode networks in devices with local gate. We also find fractional and integer Chern insulators at zero magnetic field via thermodynamic compressibility measurements at ν = +2/3 and +1. These findings open new possibilities for hybrid interfaces between superconductors and topological edge states in the low-disorder limit.

• Title: Transport evidence for chiral surface states from 3D Landau bands

• Speaker: Dr. Junho Seo (Max Planck Institute , Germany)

• Date & Time / Venue: December 23th (Mon.), 2024,  3:30 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Strong magnetic fields in metals confine electrons into Landau orbits, except at the boundaries, where frequent surface collisions disrupt their cyclotron motion. In two-dimensional (2D) systems, these boundary states form dissipationless chiral edge channels in the quantum Hall regime. In contrast, the quantum limit of three-dimensional (3D) metals is traditionally thought to differ fundamentally due to gapless Landau bands, lacking quantized Hall conductance or dissipationless transport. Yet, akin to the 2D case, also 3D semiclassical electron trajectories at the surfaces parallel to the magnetic field cannot complete cyclotronic motion and yield skipping orbits. In the quantum limit, these skipping orbits form chiral surface states, 3D analogs of quantum Hall states in 2D. In this talk, I will demonstrate enhanced surface conduction in the quantum limit of the 3D semimetal bismuth through micro-patterning, characterized by the counterintuitive increase in conductivity as material is removed. The conductance of 3D chiral surface states naturally accounts for this behavior and the highly non-local transport observed in micron-sized crystalline bismuth structures. These findings introduce a new approach to engineering and exploiting chiral conduction on the surfaces of 3D materials, offering a vast design space for geometries beyond the simple 1D boundary modes of 2D systems.

• Title: Orbital magnetism in spin compensated double perovskites

• Speaker: Prof. Ji Hoon Shim (POSTECH)

• Date & Time / Venue: November 28th (Thu.), 2024,  4:50 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Orbital magnet where only orbital contribution constitutes magnetism of materials would be utilized promisingly in orbitronics in terms of easy electric control and controlling orbital degree of freedom. Most of conventional antiferromagnet have not quite paid attention to orbital magnetic moment considering spin part leadingly. Here, we revisited half-metal antiferromagnet in the sense that its spin polarization comes from existence of inequivalent magnetic sublattice. Among them, we focused on spin and orbital magnetic moments of double perovskite using DFT+U+SOC calculations after suggesting design rules for orbital magnet in double perovskite categorized into four cases. Combination of d orbital occupancies of magnetic ions is a key descriptor for designing them and further considerations of Hund's rule and combination of transition metals determine type of orbital magnetism. Also, calculations of orbital exchange energy and electronic structure verify that orbital magnetism can be controlled easily such as doping and electric control.

• Title: Ultrafast spectroscopy study on collective modes of charge-density-wave materials

• Speaker: Prof. Soyeun Kim (DGIST)

• Date & Time / Venue: November 28th (Thu.), 2024,  3:30 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : One of the major goals of condensed matter physics is to understand the novel phase transition mechanism where various degrees of freedom are strongly coupled. Measuring quasiparticles intrinsic to the phase, such as phonons and magnons, is therefore a good way to monitor and diagnose the phase of solids. In this talk, we discuss various collective modes that arise in quantum materials hosting charge-density-wave (CDW) phases originating from strong charge-lattice coupling. We first investigate a non-magnetic chiral chain lattice system in (TaSe4)21, which exhibits incommensurate CDW phase transition near 260 K. As highlighted a few years ago [1], the coexistence of CDW wavevector and Weyl fermions suggested that (TaSe4)21 may host quasiparticle that follows axion-like electrodynamics that allows E.B in analog with axion particles in high-energy physics, which is yet controversial [2]. An important thing to point out is that much basic information about CDW modes in (TaSe4)21 has been unclear despite the intense amount of research over the past few decades. Some recent advancements of different types of collective modes explored via ultrafast spectroscopy, including massive phason [3] and composite amplitude modes [4], will be discussed. In the second part, we investigate the quasi-1D CDW phase in a two- dimensional lattice of TbTe3 where external uniaxial strain is applied. Here we will estimate the phenomenological free energy potential state of the CDW phase by monitoring the CDW order parameters [5]. Our approaches using femtosecond light pulses shed light on elusive collective mode detection that was inaccessible before, thereby demonstrating the essential role of ultrafast spectroscopy in resolving complex electronic and lattice structures in quantum materials.
  
  [1] J. Gooth et al., Nature 575, 315 (2019)
  [2] A. A. Sinchenko et al., Appl. Phys. Lett. 120, 063102 (2022)
  [3] S. Kim et al., Nat. Mater. 22, 429 (2023)
  [4] Q.L. Nguyen, R. Duncan et al., Phys. Rev. Lett. 131, 076901 (2023)
  [5] S. Kim et al., Rep. Prog. Phys. 87, 100501 (2024)

• Title: Atomic-scale Imaging of Valence Electron Motion in Solids

• Speaker: Prof. David A. Reis (Stanford Univ. and SLAC)

• Date & Time / Venue: December 4th (Wed.), 2024,  4:00 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Much of materials’ properties depend on the atomic-scale structure and dynamics of the outermost valence electrons of its constituent atoms.  Nonetheless, the optical properties of materials at the relevant energy scale of valence electron motion involves a macroscopic average over the atomic-scale structure, as the wavelength of light is orders of magnitude larger than the spacing between atoms.  This led to the constitutive relations describing macroscopic electrodynamics in terms of frequency dependent electric permittivity and magnetic permeability of materials, and their related susceptibilities. For small perturbation the response is linear in the applied fields, and the concept of superposition holds, but in general the interaction is strong enough that nonlinearities can become ubiquitous under intense laser excitation.  While the macroscopic linear and nonlinear response are constrained by various microscopic symmetries, and first principles, quantum calculations can often predict the behavior with high accuracy, experimentally the microscopic optical response remains largely elusive.
  For well over a century, x rays have been used to probe the atomic scale structure of matter, due to their short wavelength, relatively weak interaction with matter and penetrating power.  In the last decade and a half, x-ray free-electron lasers (XFELs) have emerged as powerful probes not just of structure but also the dynamics of matter on the relevant length and time scales of atomic (and more recently electronic) motion matter.   Even with the unprecedented intensity of XFELs, the measurement of valence electron motion is still challenging since these electrons tend to be delocalized and a small fraction of the total electron density.  Here we will describe recent results on x-ray scattering from optically-driven crystals, where phase-matched nonlinear sum frequency generation is particularly sensitive to the valence electron motion within a unit cell.  In this case the scattered x rays appear as sidebands in energy and momentum about the ordinary elastically scattered Bragg peaks and their amplitude is proportional to the magnitude square of the spatial and temporal Fourier components of the driven charge density [1-4]. We present measurements of the first and second order sidebands in single crystal silicon excited below the band gap [5]. We find that the polarization dependence of the second order sideband from a single Bragg peak already reveals important information about the local symmetry of the interstitial electrons, even without knowing the phase of the nonlinear structure factors.  Extension of this method to imperfect crystals will allow us to probe the microscopic origins of the strong-field and far-from equilibrium response in a variety of materials. We will thus also describe proof-of-principal x-ray and optical mixing measurements on MgO using a purpose-built monochromator and analyzer on the PAL-XFEL this past January, and plans for new measurements beginning later this week [6].
  
  References
  [1] P. M. Eisenberger and S. L. McCall. Phys. Rev. A, 3, 1145, 1971.
  [2] I. Freund and B. F. Levine. Phys. Rev. Lett., 25, 1241, 1970.
  [3] T. E. Glover, D. M. Fritz, M. Cammarata, T. K. Allison, et al., Nature, 488,7413, 603, 2012.
  [4] D. Popova-Gorelova, D. A. Reis, and R. Santra. Phys. Rev. B, 98, 224302, 2018.
  [5] C. Orenelis-Skarin et al., in progress 2024.
  [6] C. Orenelis-Skarin et al., PAL-XFEL proposal numbers 2023-2nd-XSS-031 and 2024-2nd-XSS-022.
  
  Acknowledgment: This work was supported by the AMOS program within the Chemical Sciences, Geosciences, and Biosciences: Division, U.S.  Department of Energy. We acknowledges the support of the LCLS and PAL-XFEL, and past support from SACLA and SwissFEL where preliminary results were obtained.  This work was the effort of a number of very talented people.  Please see the talk for a full list of collaborators.
  
  

• Title: Optical Metasurfaces: a new approach for Beam shaping, Sensing and Authentication

• Speaker: Prof. Jacob Scheuer (Tel-Aviv University)

• Date & Time / Venue: October 30th (Wed.), 2024, 2:00 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Metasurfaces are one of the focal area of current research in optics and photonics, mainly because of their ability to control and manipulate many of the properties of electromagnetic waves: Amplitude, Phase and Polarization. These capabilities can potentially pave the way for new types of photonic devices and applications ranging from flat-optics and holography to sensing and telecommunications. In this presentation I will review the research carried out on metasurfaces at the my group in Tel-Aviv University. I will review the fundamental properties of metasurfaces and their design approach, and discuss several potential applications in beam shaping, sensing and authentication.

• Title: Unconventional functional states by synthetic crystal symmetries

• Speaker: Prof.  Daesu Lee (POSTECH)

• Date & Time / Venue: October 31th (Thu.), 2024,  4:50 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Controlling spatial symmetries, such as inversion and mirror symmetry, on demand in quantum materials is becoming increasingly crucial. However, challenges like fundamental incompatibilities and the lack of effective techniques remain significant obstacles. Using complex oxides as a model system, this talk presents two novel concepts to manipulate crystalline symmetries for electronic functions beyond conventional methods. The first part presents "synergistic polar states by selective atomic gradient,” a strategy to universally achieve strong bulk polar state, allowing the coexistence of previously incompatible properties like metallicity. This unusual coexistence synergistically leads to exceptional functionalities, including bulk Rashba metal with tunable nonreciprocal transport, high-k dielectricity with an equivalent oxide thickness below 0.1 nm, and giant pyroelectricity. The second part of this talk explores “deterministic crystal rotation by ferroelastic writing," a concept that uses mechanical stress via atomic force microscopy to precisely control and eliminate structural heterogeneity in crystal orientations. This enables a fully-three- dimensional nanoscale design of domain textures, including artificial chiral/spiral structures, and allows for mechanical writing and erasing of magnetic structures, enhancing electronic and spintronic functionalities. 

• Title: Symmetry analysis and electronic structure of altermagnetic systems

• Speaker: Prof. Chang-Jong Kang (Chungnam National University)

• Date & Time / Venue: October 31th (Thu.), 2024,  3:30 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Altermagnetism is a recently identified fundamental form of magnetism characterized by a vanishing net magnetization and a broken electronic structure with time-reversal symmetry. In this talk, we employ a combination of symmetry analysis and first-principle calculations to reveal that the crystallographic symmetry groups of numerous magnetic materials, featuring negligibly small relativistic spin-orbit coupling (SOC), are significantly larger than conventional magnetic groups. Consequently, a symmetry description incorporating partially decoupled spin and spatial rotations, termed the spin group, becomes essential. We establish the classifications of spin point groups that describe collinear magnetic structures, encompassing altermagnetic phases. Using MnTe as an example, we provide direct evidence for altermagnetism in MnTe.

• Title: Enhanced light-electron interactions via plasmonic metasurfaces

• Speaker: Prof. Jacob Scheuer (Tel-Aviv University)

• Date & Time / Venue: October 23th (Wed.), 2024,  4:00 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Manipulating and controlling the properties of free electrons by light is attracting much attention as this approach facilitates new studies and applications in both the classic and quantum regimes. Enhancing such interactions requires the generation of intense and often highly localized fields. An attractive approach for generating such intense fields is by illuminating a surface which is patterned by sub-wavelength nanostructures. Theses nanostructures could be metallic (plasmonic) or dielectric, where each type has its own advantages and drawbacks. Plasmonic structures exhibit Ohmic losses at optical frequencies but are simpler to fabricate, particularly in deep sub-wavelength dimensions, thus offering a new paradigm for manipulation of particle beams adjacent to the surface. In this talk we will present plasmonic metasurfaces as an attractive platform for electron-beam manipulation, particularly for acceleration of sub-relativistic particles as well as a potential tunable source based on Cherenkov-Smith-Purcell radiation. Compared to the more established dielectric laser accelerators, the metasurface laser accelerators exhibit lower net acceleration gradient but improved efficiency and simpler realization, rendering them attractive for applications where lower power and compact dimensions are important.

• Title: 2024 Snail Lectures III: Phase transitions in the early Universe

• Speaker: Tae Hyun Jung (CTPU, IBS)

• Date & Time / Venue: September 28th (Sat.), 2024,  12:30 - 8:00 PM / 5th floor, KIAS

• Abstract
  : In this lecture, I will briefly introduce phase transitions in the early Universe for the target audience of graduate students who are familiar with quantum field theory and early Universe cosmology. The lecture will be composed of three parts. In the first part, the thermal effective potential will be introduced and I will explain its physical meaning and how we calculate it. Then I will explain phase transitions in the early Universe, especially focusing on first-order phase transitions. The last part of the talk is about their applications in BSM physics and discussion.
  
  12:30 - 13:30  Registration
  13:30 - 15:00  Lecture 1: Thermal effective potential
  15:00 - 15:15  Questions and Coffee Break
  15:15 - 16:30  Lecture 2: Phase transitions in the early Universe
  16:30 - 16:45  Questions and Coffee Break
  16:45 - 18:00  Lecture 3: BSM applications
  18:00 - 20:00  Dinner

• Title: Strong phonon-assisted luminescence processes in hexagonal boron nitride

• Speaker: Prof. Jonghwan Kim (Department of Materials Science and Engineering, POSTECH)

• Date & Time / Venue: September 26th (Thu.), 2024, 4:50 PM/ Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Hexagonal boron nitride (hBN) is a van der Waals (vdW) semiconductor with a wide bandgap of ~5.96 eV. Despite the indirect bandgap characteristics of hBN, charge carriers excited by high energy electrons or photons efficiently emit luminescence at deep-ultraviolet (DUV) frequencies via strong electron-phonon interaction. In this work, we probe luminescence processes at a band edge in hBN by means of optical imaging and spectroscopy at deep ultraviolet frequencies. Our laser excitation spectroscopy shows that carrier excitation processes and radiative recombination processes sensitively depend on stacking orders of hBN. In addition, we demonstrate prominent electroluminescence and photocurrent generation from hBN by fabricating vdW heterostructures with graphene electrodes. Our work provides a pathway toward efficient DUV light emitting and detection devices based on hBN.

• Title: The Hidden Ferro-rotational Density Wave and Axial Higgs from RTe3's Quantum Geometry

• Speaker: Prof. Kenneth S. Burch (Department of Physics, Boston College)

• Date & Time / Venue: September 26th (Thu.), 2024, 3:30 PM/ Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Detecting unconventional density waves and identifying their underlying mechanism has proven particularly challenging. Here, I will discuss our discovery of a rare ferro-rotational CDW order from orbital modulation requiring a nontrivial order parameter. Using Raman spectroscopy and quantum interference, we revealed the first Axial Higgs mode associated with charge order. Additional Raman, Second Harmonic, and Scanning Transmission Electron Microscope experiments establish this occurs in a density wave that breaks all vertical mirrors but maintains inversion symmetry. The Raman and Mu-SR experiments further confirm the absence of time-reversal symmetry breaking. I will discuss how this can be explained by a rare combination of orbital and charge order that results from the unique quantum geometry of Rare-Earth Tritellurides.

• Title: Quenched Pair Breaking by Interlayer Correlations as a Key to Superconductivity in La3Ni2O7

• Speaker: Dr. Siheon Ryee (University of Hamburg, Germany)

• Date & Time / Venue: September 30th (Mon.), 2024, 3:00 PM/ Physics Seminar Room (Bldg.3, #302)

• Abstract
  : The recent discovery of superconductivity with Tc ~ 80 K in the bilayer nickelate La3Ni2O7 under high pressure heralds a new class of high-Tc superconductors. The most notable feature of this material is a strong interlayer electronic coupling unlike many unconventional superconductors. In this respect, central questions concern “How does the interlayer coupling affect the low-energy physics?" and “Is the interlayer coupling a friend or foe of superconductivity?". In this talk, I will demonstrate using a cluster dynamical mean-field theory that nonlocal self-energy driven by the interlayer coupling in La3Ni2O7 induces a Lifshitz transition of Fermi surface topology. By solving a relevant gap equation, I will further argue that superconductivity is promoted by this “dimer” electronic correlation. The underlying mechanism is the quenching of a strong pair-breaking channel resulting from the Fermi surface change. This picture provides a possible reason of why superconductivity emerges only under high pressure.
  Reference: S. Ryee, N. Witt, and T. O. Wehling, Phys. Rev. Lett. 133, 096002 (2024)

• Title: 진공 요동의 시간적 제어:  새로운 비평형 빛-물질 상호작용

• Speaker: Prof. Bumki Min (KAIST)

• Date & Time / Venue: September 4th (Wed.), 2024, 4:00 PM/ Physics Seminar Room (Bldg.3, #302)

• Abstract
  : 원자의 자발 방출 붕괴 현상은 원자 및 분자 물리학, 광학, 그리고 광자학 분야에서 핵심적인 역할을 담당한다. 양자 전기역학 관점에서, 원자의 자발 방출 붕괴 현상은 진공요동과 원자 간의 상호작용으로 설명할 수 있으며, 유도 방출 붕괴와 함께 물질의 빛 방출 과정의 두 가지 주요 메커니즘을 구성한다.
  20세기 초 양자 물리학의 태동 이후 40여 년 동안 원자의 자발 방출 붕괴율은 불변하는 고유 성질로 여겨졌다. 그러나 1946년 에드워드 퍼셀의 연구는 이 개념에 혁신적인 변화를 가져왔다. 퍼셀은 자발 방출 붕괴율이 원자 주변의 공간적 광학 환경, 즉 빛의 국소 상태 밀도에 따라 제어될 수 있음을 이론적으로 입증하였다. 이후 약 40년 동안 이 이론은 실험적 검증과 이론적 확장을 거치며 발전해 왔으며, 1987년 일라이 야블로노비치에 의해 현대적으로 재해석되고 발전되어 현재까지 광자학 분야의 연구 방향을 주도하고 설정해왔다. 그 결과, 광결정, 플라즈모닉스, 메타물질과 같은 미세 광학 구조를 활용한 자발 방출 붕괴 과정의 정밀 제어(억제와 향상) 연구가 광범위하게 진행되었으며, 이는 고효율 LED, 단일광자 광원, 양자 메모리 등의 실용적인 기술 발전으로 이어졌다.
  본 발표에서는 지난 세기 동안 진행된 선도적 연구를 한 차원 더 확장하여, 시간적(시변) 광학 환경을 이용한 비평형 빛-물질 상호작용 제어라는 광학의 새로운 연구 분야에 대해 이야기하고자 한다. 시변 환경을 이용한 제어는 기존의 정적인 공간적 제어와는 근본적으로 다른 비보존적이고 비평형적인 접근법이며 이는 빛-물질 상호작용에 대한 우리의 이해를 근본적으로 변화시킬 잠재력을 지니고 있다.

• Title: Hydrodynamic Effects in Electron Fluids on Spintronics

• Speaker: Prof. Sadamichi Maekawa (RIKEN Center for Emergent Matter Science, Japan)

• Date & Time / Venue: July 22th (Mon.), 2024, 4:00 PM/ Physics Seminar Room (Bldg.3, #302)

• Abstract
  : In metals with disorder, the electron transport is described as diffusive.  On the other hand, in those with electron-electron interaction being the dominant source of scattering, the motion of the electrons resembles the flow of classical liquids with shear viscosity, namely, the hydrodynamic fluids.  The recent progress of nano-technology has made it possible to extend the study on such hydrodynamic electron fluids in nano-devices and low dimensional materials.  In such fluids, the angular momentum of the fluid vorticity and electron spins couple each other due to the angular momentum conservation, i.e., the spin-vorticity coupling [1].  Combining the Novier-Stokes and the spin diffusion equations in the presence of the spin-vorticity coupling, we examine a variety of spintronic phenomena [2-5]. We present that metals with nano-structure provide unique spintronic devices due to the local hydrodynamic nature. The hydrodynamic phenomena of electron fluids open a door to "Hydrodynamic spintronics" .
  
  [1] M. Matsuo, E. Saitoh and S. Maekawa, Chapter 25 in “Spin Current” ed. S. Maekawa et al. (Oxford University Press, 2017).
  [2] J.Fujimoto, W.Koshibae, M.Matsuo and S.Maekawa, Phys. Rev. B103, L220404 (2021).
  [3] F.Lange, S.Ejima, J.Fujimoto, T.Shirakawa , H.Fehske, S.Yunoki and S. Maekawa, Phys. Rev. Lett. 126, 157202 (2021).
  [4] G.Okano, M.Matsuo, Y.Ohnuma, S.Maekawa, and Y.Nozaki, Phys. Rev. Lett. 122, 217701 (2019).
  [5] S. Maekawa, et al., J. Appl. Phys. 133, 020902 (2023).

• Title: Theoretical calculations for the orbital Hall effect and its magneto-optical detection

• Speaker: Dr. Daegeun Jo (POSTECH)

• Date & Time / Venue: July 8th (Mon.), 2024, 3:00 - 4:00 PM/ Physics Seminar Room (Bldg.3, #302)

• Abstract
  : The orbital and spin angular momenta of electrons are two fundamental components that bring about the magnetic properties of atoms. Nevertheless, the dynamics of orbital angular momentum in non-equilibrium has remained largely unexplored, primarily due to the belief that the orbital angular momentum may play a minor role in crystalline solids because of orbital quenching. However, recent studies have revealed that a significant orbital current can be generated by the electric field even without spin-orbit coupling, a phenomenon known as the orbital Hall effect. It has given rise to the burgeoning field of orbitronics, which aims to harness the orbital angular momentum for magnetic device applications. In this talk, we will present theoretical and numerical calculations for the orbital Hall effect. We investigate the orbital Hall effect in real materials and discuss how to detect it through magneto-optical measurements.

• Title: Holography 2024: Correlation and Entanglement in Quantum matter

• Speaker: Prof. Andrew Lucas (University of Colorado), Prof. Sebastiano Peotta (Aalto University), Prof. Ping Gao (Rutgers University), Prof. Zhenbin Yang (Tsinghua University)

• Date & Time / Venue: August 10th (Sat) - 18th(Sun), 2024/ APCTP (HogilKim Memorial Bldg., #501)

• Hompage : https://sites.google.com/view/apctpfocusprogram2024/home

• Title: 2024 Snail Lecture II - Phenomenology of Axion-like particles

• Speaker: Prof. Kingman Cheung (National Tsing Hwa University, Taiwan)

• Date & Time / Venue: July 5th (Fri.), 2024,  3:00 - 6:00 PM / Room 505, Bldg. 23, Konkuk University, Korea

• Abstract
  : This lecture will delve into the fascinating realm of axion-like particles (ALPs), theoretical extensions of the Peccei-Quinn mechanism initially proposed to solve the strong CP problem in quantum chromodynamics. Over two hours, we will explore the phenomenological aspects of ALPs, emphasizing their theoretical foundations, production mechanisms, and potential implications in cosmology and particle physics. Key topics will include the properties of ALPs, their interactions with standard model particles, and their role in dark matter and astrophysical phenomena. We will also examine current experimental searches and observational constraints, highlighting recent advancements and future prospects in the quest to detect these elusive particles. The lecture aims to provide a comprehensive overview of ALP phenomenology, offering insights into their significance in advancing our understanding of fundamental physics. 

16:00 -- 16:50   Lecture 1

16:50 -- 17:10   Break & Discussion

17:10 -- 18:00   Lecture 2

18:00 -- 20:00   Dinner 

• Title:First-principles study of novel magnetic properties in strongly correlated materials

• Speaker: Prof. Hyowon Park (University of Illinois at Chicago/ Argonne National Laboratory)

• Date & Time / Venue: June 28th (Fri.) 11:00 AM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Strongly correlated materials exhibit novel magnetism due to the complex coupling between their localized magnetic moments and neighboring electronic/magnetic degrees of freedom. First-principles studies of such materials have been challenging since the widely used density functional theory (DFT) method often fails to capture the strong correlation effect of magnetism. Here, I will show that advanced methods beyond DFT can be successfully applied to various novel magnetic materials capturing the strong correlation effect. First, I will discuss the microscopic origin of a large anomalous spin Hall effect measured in the CoNb3S6 compound, where Co ions are intercalated between NbS2 layers forming a triangular lattice [1]. The Berry curvature calculation based on the DFT+Hartree-Fock band structure can show that the non-coplanar antiferromagnetic spin ordering is crucial to produce such a large anomalous Hall conductivity [2]. Second, I will show that the leading magnetic instability of CoNb3S6 obtained from the spin susceptibility and Fermi surface calculations using dynamical mean field theory (DMFT) is consistent with the 3q magnetic structure as expected from the non-coplanar antiferromagnetic ordering [3]. Finally, I will discuss the dynamical fluctuation effect of DMFT on the correlated electronic structure of Na3Co2SbO6 in a honeycomb lattice [4], which has been suggested as a possible candidate to realize Kitaev spin liquid [5].
  
  References
  [1] N. J. Ghimire et al, Nature Communication 9, 3280 (2018)
  [2] H. Park et al, Phys. Rev. Materials 6, 024201 (2022)
  [3] H. Park et al, Phys. Rev. B 109, 085110 (2024)
  [4] N. Nguyen et al, manuscript in preparation
  [5] H. Liu et al, Phys. Rev. Lett. 125, 047201 (2020)
  
  Bio: Hyowon Park is an associate professor at the University of Illinois at Chicago (UIC) and has a joint appointment with the Argonne National Laboratory. Prior to joining UIC, he obtained his Ph.D from Rutgers University and was a post-doc at Columbia University. His research is focused on studying the theoretical understanding of various strongly correlated materials using advanced first-principle methods.

• Title: Identification of massive entanglement in many-body systems

• Speaker: Prof. Eun-Gook Moon (KAIST)

• Date & Time / Venue: June 20th (Thu.) 4:00 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Unconventional quantum many-body states may host massive entanglement, and their identification is one of the most significant problems in physics. In this seminar, we discuss one of the ways to identify the existence of the massive entanglement of many-body states such as quantum spin liquids.
  We argue that intriguing interplay between symmetry and topology may be utilized for the identification. We also discuss plausible experiments in two and three dimensional quantum magnets to identify the massive entanglement.

• Title: Magnetic field driven scalar-to-axial Higgs mode transition in charge-density wave compounds

• Speaker: Dr. Dirk Wulferding (IBS-Seoul National University)

• Date & Time / Venue: June 13th (Thu.) 4:00 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Recently, the elusive axial Higgs mode was discovered in the layered van-der-Waals material GdTe3 with a unidirectional charge-density wave (CDW) through Raman spectroscopy at ambient conditions [1]. Its axial nature is manifested by a CDW amplitude mode with a two-fold rotational periodicity, and requires the spontaneous breaking of two symmetries simultaneously. Yet, the exact symmetries involved in this process remain hidden. We present a polarization-resolved comparative Raman spectroscopy study on the two sister compounds GdTe3 (with low-temperature antiferromagnetic order) and LaTe3 (lacking any magnetic order) at various temperatures and with applied magnetic fields. The two-fold rotational periodicity of the Higgs amplitude mode is persistently observed in both materials, ruling out spin degrees of freedom as a relevant ingredient to achieve axial nature. Remarkably, we observe a dramatic increase in Higgs-mode intensity with applied magnetic fields that is linear-in-B, together with a 90° phase shift of its two-fold periodicity with field-reversal. Our observations suggest that RTe3 compounds realize an exotic charge-density wave phase with broken time reversal symmetry, that allow for an in-situ field-tuning of the Higgs mode's axiality.
  
  [1] Y. Wang et al., Nature 606, 896 (2022).

• Title: New high Tc superconductivity and symmetric pseudogap metal in the bilayer nickelate La3Ni2O7

• Speaker: Dr. Hanbit Oh (Johns Hopkins Univ.)

• Date & Time / Venue: June 11th (Tue.) 4:00 PM / Physics Seminar Room (Bldg.3, #302)

• Abstract
  : Recently, a new class of superconductor with Tc=80K was found in bilayer nickelates La3Ni2O7 under high pressure, being of significant interest in the condensed matter community. These materials present a unique platform for high-Tc superconductivity due to the nature of the bilayer and multi-orbital feature, setting them apart from any presenting nickelates and cuprates system. At this moment, a pressing challenge is to unravel the intriguing pairing mechanism underlying superconductivity in these materials and elucidate how they differ from old cuprate physics. In the first part of the talk, I will present the role of Hund's coupling as a potential key factor for understanding the remarkably high Tc of La3Ni2O7 [1]. Specifically, I will demonstrate that the minimal model is derived as a bilayer type-II t-J model within a large Hund-coupling limit, as opposed to the conventional single-orbital bilayer t-J model, where localized dz2 orbitals are simply integrated out. Notably, the type-II t-J model retains even under the charge-transfer limit, while the spin one-half degree of freedom is Zhang-Rice doubloon state [2]. In the second part of the talk, I will address a fundamental question: Can a small Fermi surface phase, which violates the Luttinger theorem, exist and give rise to superconductivity? By introducing a novel controlled theory based on a bilayer model—the ESD t-J model—we demonstrate the viability of such a scenario [3]. Furthermore, we elucidate that the small Fermi surface transitions into an inter-layer s-wave superconductor at low temperature through Feshbach resonance with a virtual Cooper pair, with a surprising doping-induced crossover from Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) at higher hole doping levels. Applying our theoretical framework, we provide a plausible scenario for the La3Ni2O7 materials.
  
  [1] Hanbit Oh and Ya-Hui Zhang, Phys. Rev. B 108 (2023)
  [2] Hanbit Oh, Boran Zhou, Ya-Hui Zhang, arXiv:2405.00092 (2024)
  [3] Hui Yang*, Hanbit Oh*, Ya-Hui Zhang, arXiv:2309.15095 (2023)Top of Form

• Title: Seebeck effect on a weak link between two charge Kondo circuits

• Speaker: Prof. Thi Kim Thanh Nguyen (Vietnam Academy of Science and Technology)

• Date & Time / Venue: June 3rd (Mon.) 4:00 PM / #512, APCTP

• Abstract
  : We propose a model describing the Seebeck effect on a weak link between two quantum systems with fine-tunable ground states of Fermi and non-Fermi liquid origin. The experimental realization of the model can be achieved by utilizing the quantum devices operating in the integer quantum Hall regime [Z. Iftikhar et al., Nature (London) 526, 233 (2015)] designed for detection of macroscopic quantum charged states in multichannel Kondo systems. We present a theory of thermoelectric transport through hybrid quantum devices constructed from quantum-dot quantum-point-contact building blocks. We construct a full- fledged quantitative theory describing crossovers between different regimes of the multichannel charge Kondo quantum circuits and discuss possible experimental realizations of the theory. High controllability of the device allowing to fine tune the system to different regimes described by multichannel and multi- impurity Kondo models is also discussed.

• Title: Mechanical characterization of ferromagnetic resonance in magnomechanical hybrid devices

• Speaker: Hiroshi Yamaguchi (NTT Basic Research Laboratories, Japan)

• Date & Time / Venue: June 11th (Tue.) 1:30 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Magnon has been attracting increasing attention from the viewpoints of both fundamental study and technological applications. This is because of the unique properties of magnons, such as nanometer wavelengths, wide frequency ranges from GHz to low THz, high tunability, and Joule heat-free propagation. Their use holds promise for developing compact, high-speed, and low-power-consumption devices for wireless telecommunications and hardware-based reservoir computing as well as studying quantum information technology. Acoustic phonons at microwave frequencies are promising candidates for the interface between magnons and other excitations because of their micro- and nanometer wavelength and negligible radiation loss. In this talk, I will introduce our recent activities on magnomechanical hybrid devices using SAW-resonators [1] and phononic crystal cavities [2], where the acoustic resonator can be used as a novel tool for studying the ferromagnetic resonance.
  
  [1] D. Hatanaka, M. Asano, H. Okamoto, Y. Kunihashi, H. Sanada, and H. Yamaguchi, "On-Chip Coherent Transduction between Magnons and Acoustic Phonons in Cavity Magnomechanics", Phys. Rev. Appl. 17 (3), 034024 (2022).
  [2] D. Hatanaka, M. Asano, H. Okamoto, and H. Yamaguchi, "Phononic Crystal Cavity Magnomechanics", Phys. Rev. Appl. 19, 054071 (2023).

• Title: Thermodynamics in the 21st century

• Speaker: Prof. Hyunggyu Park (Quantum Universe Center, KIAS)

• Date & Time / Venue: May 31st (Fri.) 3:00 - 4:00 PM / #512, APCTP

• Abstract
  : Thermodynamics is one of the oldest subjects in physics. Over the last two decades, thermodynamics has been rejuvenated with a few theoretical breakthroughs in deeper understanding of the thermodynamic second law. A new framework, called as stochastic thermodynamics, emerges as a practical tool to calculate fluctuations of thermodynamic quantities, which are crucial in controlling the operation of small devices like molecular motors. In this talk, I will briefly sketch these breakthroughs, in particular, fluctuation theorems and thermodynamic uncertainty relations. If time permits, I will discuss the classical speed limit and tight finite-time Landauer's bound as an example.

• Title: Chirality knob: from molecules to hybrid organic-inorganic metal halides

• Speaker: Dr. Alessandro Stroppa (Research Director of the CNR-SPIN Institute (Italy) & Deputy director of the research unit in L’Aquila (Italy))

• Date & Time / Venue: May 24th (Fri.) 10:00 AM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Square-lattice antiferromagnets are considered as a promising platform for realizing exotic quantum magnetic phases, including quantum spin liquid and valence bond solid state [1]. Deviations from the spin-wave theory observed in inelastic spectra of various squarelattice cuprates have been interpreted as precursors of quantum magnetic phases [1]. Recently, our group established a spin nematic phase in the square-lattice iridate Sr2lrO4 [2]. Here, a complete breakdown of coherent magnon excitations at short-wavelength scales suggests many-body entanglement within the antiferromagnetic state. Additionally, we discover that incoherent magnetic excitations become prevalent upon heterointerfacing two distinct types of antiferromagnets [3]. These findings are based the successful development of an end-station for resonant inelastic x-ray scattering at the 1C beam line of Pohang Light Source-II [4].
  
  [1] H. Shao et al., Phys. Rev. X 7, 041072 (2017).
  [2] Hoon Kim*, Jin-Kwang Kim* et al., Nature 625, 264-269 (2024).
  [3] Jin-Kwang Kim*, Hoon Kim*, Junyoung Kwon* et al., unpublished.
  [4] Jin-Kwang Kim et al., J. Synchrotron Rad. 30, 643-649 (2023).

• Title: Chirality knob: from molecules to hybrid organic-inorganic metal halides

• Speaker: Dr. Alessandro Stroppa (Research Director of the CNR-SPIN Institute (Italy) & Deputy director of the research unit in L’Aquila (Italy))

• Date & Time / Venue: May 24th (Fri.) 10:00 AM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Chirality is an important structural property: right-handed and left-handed chiral materials have identical chemical composition and connectivity, but they are related by mirror transformation, forming a couple of enantiomers. Chiral materials show unique features: the intrinsic non-centrosymmetry leads to optical rotation, circular dichroism (CD), second-harmonic generation (SHG), piezoelectricity, pyroelectricity, ferroelectricity, and topological quantum properties. In this talk, I will discuss the intriguing interplay between chirality and physical properties in innovative materials, ranging from molecules, twisted bilayers (non-magnetic as well magnetic) to chiral hybrid organic-inorganic perovskites. We will see that it is possible to “generate” and “tune” chirality in such a way that it can be view as a new “knob” for physical properties of the materials.

• Title: Magnetic field driven scalar-to-axial Higgs mode transition in charge-density wave compounds

• Speaker: Dr. Dirk Wulferding (IBS-Seoul National University)

• Date & Time / Venue: June 13th (Thu.) 4:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Recently, the elusive axial Higgs mode was discovered in the layered van-der-Waals material GdTe3 with a unidirectional charge-density wave (CDW) through Raman spectroscopy at ambient conditions [1]. Its axial nature is manifested by a CDW amplitude mode with a two-fold rotational periodicity, and requires the spontaneous breaking of two symmetries simultaneously. Yet, the exact symmetries involved in this process remain hidden. We present a polarization-resolved comparative Raman spectroscopy study on the two sister compounds GdTe3 (with low-temperature antiferromagnetic order) and LaTe3 (lacking any magnetic order) at various temperatures and with applied magnetic fields. The two-fold rotational periodicity of the Higgs amplitude mode is persistently observed in both materials, ruling out spin degrees of freedom as a relevant ingredient to achieve axial nature. Remarkably, we observe a dramatic increase in Higgs-mode intensity with applied magnetic fields that is linear-in-B, together with a 90° phase shift of its two-fold periodicity with field-reversal. Our observations suggest that RTe3 compounds realize an exotic charge-density wave phase with broken time reversal symmetry, that allow for an in-situ field-tuning of the Higgs mode's axiality. [1] Y. Wang et al., Nature 606, 896 (2022).

• Title: Predicting spin-phonon dynamics in quantum materials from first-principles

• Speaker: Dr. Jinsoo Park (University of Chicago)

• Date & Time / Venue: May 20th (Mon.) 4:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Understanding the dynamical process involving electrons, spins, and lattice vibrations (phonons) is key to developing the next generation of quantum materials and devices. A special role is played by the spin-phonon interactions as they limit the performance of devices based on spins. However, its quantitative analysis remains an open challenge. The spin-orbit coupling causes various dynamical phenomena that couples with phonons, such as spin-flip scattering and spin precession — commonly known as the Elliott-Yafet and Dyakonov-Perel mechanisms — which are difficult to capture in modern quantum materials with increasing complexity.
  In this talk, I will introduce a theoretical framework that unifies the two mechanisms and a computational platform that can investigate their physics in a wide range of quantum materials. I will first show a first-principles workflow that can capture the interactions between electrons and phonons in the presence of spin-orbit coupling. This scheme will be combined with a many-body technique including electron-phonon interactions, allowing accurate prediction of spin relaxation in materials including key semiconductors for quantum technologies (Diamond, Si, GaAs, and WSe2). Finally, I will address challenges in calculating spin-phonon interactions in correlated electron systems, enabling the study of spin motion in Mott insulators. These developments establish a broadly applicable approach for computational prediction of spin dynamics in a wide range of materials, next-generation spintronic, and magnetic devices.

• Title: Brief overview on altermagnetism

• Speaker: Prof. Sung Hyon RHIM (University of Ulsan)

• Date & Time / Venue: May 13th (Mon.) 4:10 PM / IBS POSTECH Campus Bldg. 105

• Abstract
  : This talk aims a brief and short handed overview on altermagnetism a new magnetic phase recently proposed The altermagnetism is mostly regarded as d wave magnetism, as a counterpart of d wave superconductivity Hence, short handed summary on d wave superconductivity in terms of gap symmetry is provided As symmetry arguments are unavoidable in discussing altermagnetism operators consisting of groups, more specifically spage group and spin group, are introduced As final remark, the comparison between antiferromagentism and altermagnetism is outlined This talk does not intend a complete understanding of alter magnetism but rather sketchy and intuitive understanding of altermagnetism

• Title: Flexoelectric polarizing and control of a ferroelectric metal phase of SrRuO3 thin films

• Speaker: Prof. Se Young PARK (Soongsil University)

• Date & Time / Venue: May 13th (Mon.) 3:00 PM / IBS POSTECH Campus Bldg. 105

• Abstract
  : This talk aims a brief and short handed overview on altermagnetism a new magnetic phase recently proposed The altermagnetism iElectric polarization is well defined only in insulators, not metals, and there is no general scheme to induce and control bulk polarity in metals We circumvent this limitation by utilizing a pseudo electric field generated by inhomogeneous lattice strain, namely a flexoelectric field, as a means of polarizing and controlling a metal Using heteroepitaxy, atomic scale imaging, and first principles calculations, we show the existence of flexoelectric fields driven by the interfacial coupling between SrRuO 3 deposited on 111 oriented SrTiO 3 Sheer and longitudinal strain gradients are generated by the change in the lattice vectors associated with a gradual change in the octahedral rotation pattern from a a a around the interface to a a c 0 away from the interface We find substantial changes in electronic and magnetic properties from enhanced electron correlation associated with the Ru off center displacements, demonstrating the flexoelectric control of the electronic and magnetic propertiess mostly regarded as d wave magnetism, as a counterpart of d wave superconductivity Hence, short handed summary on d wave superconductivity in terms of gap symmetry is provided As symmetry arguments are unavoidable in discussing altermagnetism operators consisting of groups, more specifically spage group and spin group, are introduced As final remark, the comparison between antiferromagentism and altermagnetism is outlined This talk does not intend a complete understanding of alter magnetism but rather sketchy and intuitive understanding of altermagnetism

• Title: Towards reproducible moiré physics

• Speaker: Dr. Yeongjun Choi (University of California Santa Barbara)

• Date & Time / Venue: May 13st (Thu.) 4:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Moiré materials have shown a plethora of correlated phases, notably unconventional superconductivity and fractional quantum anomalous Hall effect. However, the twist-angle uncertainty during sample preparation and angle inhomogeneity as disorder have hindered the possibility of utilizing or hybridizing these exotic quantum states into a mesoscopic device. With the help of our novel techniques, we have used common imaging tools to efficiently screen and isolate the moiré lattices, yielding reproducible superconducting magic-angle graphene samples. Moreover, these versatile techniques have allowed us to produce the highest quality van der Waals samples, enabling us to study a range of correlated phenomena - from inter-valley coherent states in flat-band graphene systems, to enhanced superconductivity in spin-orbit coupling induced rhombohedral graphene, to electron hydrodynamics. Our scheme may pave the way to design experiments that could shed light on the mechanisms behind these emergent phases, as well as to fabricate complicated structures that combine the phases to reach quantum technology applications.

• Title: Phonon dynamics in flowing energy and angular momentum

• Speaker: Prof. Jongseok Lee (GIST)

• Date & Time / Venue: May 1st (Wed.) 4:00 - 5:30 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : In crystalline solids, lattice vibrations are given as quantized quasi-particles, named phonons, having well-defined energy and momentum. Their strong correlations with other degrees of freedom or other quasi-particles lead to the renormalization of phononic properties in a correlated system and also provide numerous intriguing phenomena, such as superconductivity, ferroelectricity, magnetoelastic effect, and so on. In this talk, I will discuss spatio-temporal evolutions of energy and angular momentum carried by phonons using time-resolved optical techniques. The topic will cover (i) energy transfer between electron and phonon, (ii) angular momentum transfer from spin to acoustic phonons, and (iii) phonon-mediated energy transport across nanometer-thick interface layers.

• Title: Defects and Interfaces in Critical Quantum Systems

• Speaker: Prof. Matthew Roberts (APCTP JRG Leder)

• Date & Time / Venue: April 17th (Wed.) 4:00 - 5:30 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : The study of critical quantum systems is of great interest to many branches of theoretical physics, from high energy to condensed matter. However, our starting point of quantum field theory is most often studied from an idealised fully Lorentz invariant perspective, despite the fact that many physical systems are not so clean. In recent years the generalisation of our understanding of anomalies and universality has been slowly expanding to allow for nontrivial defects that break some space-time symmetries. I will review some of my recent work in this direction. While the details of this work often involve the details of supersymmetry and string theory, the results hint towards much more general universal results.

• Title: Anomalous Statistics in Langevin Equation with Fluctuating Diffusivity : non-Gaussian yet Brownian, anomalous diffusion, and ergodicity breaking

• Speaker: Prof. Takuma Akimoto (Tokyo University of Science, Japan)

• Date & Time / Venue: April 16th (Tue.) 5:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Diffusion is a ubiquitous phenomenon in nature. The diffusion coefficient, defined by the slope of the mean square displacement, is a fundamental quantity characterizing a diffusing particle and its environment. The instantaneous diffusivity may change over time in complex systems ranging from living materials to disordered systems. This fluctuating diffusivity unexpectedly affects its global diffusion properties, such as non-Gaussian distribution in the propagator, anomalous diffusion, and trajectory-to-trajectory fluctuations of the mean square displacement. In my talk, I examine the propagator of diffusing particles, the time-averaged square displacement, and its fluctuations for several stochastic diffusion models with fluctuating diffusivities. We show that fluctuating diffusivities are pivotal in providing non-Gaussian yet Brownian diffusion, anomalous diffusion, and ergodicity breaking. These results demonstrate how fluctuating diffusivities play an essential role in providing a physical or biological function such as an efficient search, diffusion-limited reactions, formation and dissociation of protein complexes. The results not only provide a deeper understanding of the role of fluctuating diffusivities in diffusion processes but also pave the way for exploring anomalous statistics from microscopic dynamics in non-equilibrium phenomena.

• Title: Time-domain braiding of anyons

• Speaker: Prof. Heung-Sun Sim (KAIST)

• Date & Time / Venue: April 3rd (Wed) 4:00 - 5:30 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Anyons are quasiparticles in two dimensions. They do not belong to the two classes of elementary particles, bosons and fermions. Instead, they obey Abelian or non-Abelian fractional braiding statistics. There are now two sorts of experimental evidences [1-3] of braiding of Abelian anyons in the fractional quantum Hall regime at 1/3 filling. The underlying mechanism of one of the two is the time-domain braiding of anyons that has been introduced and developed by my group [3-6]. I will talk about the theory, experimental evidences, and perspective of the time-domain braiding of anyons.
  
  [1] H. Bartolomei et al., Science 368, 173 (2020).
  [2] J. Nakamura, S. Liang, G. C. Gardner, and M. J. Manfra, Nat. Phys. 16, 931 (2020).
  [3] J.-Y. M. Lee, C. Hong, T. Alkalay, N. Schiller, V. Umansky, M. Heiblum, Y. Oreg, and H.-S. Sim, Nature 617, 277 (2023).
  [4] C. Han et al., Nature Communications 7, 11131 (2016).
  [5] B. Lee, C. Han, and H.-S. Sim, Phys. Rev. Lett. 123, 016803 (2019).
  [6] J.-Y. M. Lee and H.-S. Sim, Nature Communications 13, 6660 (2022).

• Title: Paradigm For Superconducting Vortices with Non-metallic Core

• Speaker: Prof. Amit Ghosal (Indian Institute of Science Education & Research, Kolkata)

• Date & Time / Venue: March 26th (Tue.), 2024, 4:00 - 5:00 PM / Room 105, IBS POSTECH Campus Building

• Abstract
  : When a pristine and conventional type-II superconductor (SC) is exposed to an orbital magnetic field, the Abrikosov vortex lattice forms. These vortices feature a metallic core and define the standard paradigm of "vortices.” Here, we show that many SCs of interest, beyond "pristine” or "conventional,” depart from the above truism and often feature nonmetallic cores. We present novel phenomena associated with such unconventional vortices, focusing primarily on two examples.
  (a) A conventional type-II SC under simultaneous perturbations of disorder and magnetic field: For weak disorder, the critical field for suppressing the superconducting energy gap matches the critical field HC at which the superfluid density collapses. However, these two critical fields diverge from each other with increasing disorder, creating a large pseudogap region. In addition to providing a natural explanation for the gigantic magneto-resistance peak observed in disordered superconducting thin films, our phase diagram explains the disappearance of the celebrated Caroli-de Gennes-Matricon peak in disordered SCs. The role of charge modulation ordering competing with superconductivity will also be discussed.
  (b) A strongly correlated d-wave SC in the presence of an orbital field: The strong electronic repulsions at low doping promote the formation of Mott insulating vortex cores, and consistently, the local density approaches half-filling in the core region. Our calculation shows a non-monotonic variation of the vortex size as a function of doping in contrast with weak coupling descriptions. This causes an enhancement of the vortex region in the underdoped limit. The Mott-insulating vortex core has prominent effects on the local density of states, and our finding sheds light on the tunneling spectroscopic measurements in the vortex phase of cuprate superconductors. The issue of pinning vortices by impurities in a strongly correlated d-wave SC will also be discussed.

• Title: Single shot readout of the nuclear spin in a single atom using ESR-STM

• Speaker: Prof. Jinwon Lee (Department of Quantum Nanoscience, Kavli Institute of Nanoscience, Delft University of Technology)

• Date & Time / Venue: February 19th (Mon.), 2024, 4:00 - 5:00 PM / Room 105, IBS POSTECH Campus Building

• Abstract
  : Individual nuclear spins have attracted research interest as promising candidates for the building blocks for quantum memory because they have longer lifetime and coherence time compared to electronic spin states Most studies on individual nuclear spins have focused on the nuclear spins embedded in solids such as nitrogen vacancy centers in diamond and single molecule magnets, which have limited controllability due to their environment Scanning tunneling microscopy with electron spin resonance (ESR STM), which allows for precise placement of individual magnetic atoms on a crystal surface, recently observed the nuclear spin state through the hyperfine interaction However, time resolved measurements for its relevant timescales have not been reported In this work, we achieve single shot measurements of the nuclear spin state of 49 Ti atom, which has S= 1/2 (electronic) and I= 7/2 (nuclear) spins, adsorbed on MgO/Ag(001) using ESR-STM We apply the pulsed radio frequency electric field at the fixed frequency, which can drive ESR only when the atom has a certain nuclear spin state and observe whether ESR is driven or not by measuring tunneling conductance This new approach enables time resolved measurement of the nuclear spin, and we measure its intrinsic lifetime to be 5 sec, which is 7 orders of magnitude longer than the electronic spin in the same atom Moreover, we reveal the nuclear spin pumping and relaxation process by sending DC or AC field between the pulses This long lifetime of the nuclear spin together with the ability of atom manipulation offers a new platform to investigate quantum coherence and entanglement of atomic nuclear spins on surfaces.

• Title: Superspintronics: a paradigm shift for low power electronics and future directions

• Speaker: Ph.D. Jason Robinson (Univ. of Cambridge)

• Date & Time / Venue: January 30th (Tue.), 2024, 4:00 PM / Science Bldg Ⅰ, #202

• Abstract
  : Superconductors carry charge in the absence of Ohmic dissipation, but since the Cooper pairs of electrons have antiparallel spins in a singlet state, singlet supercurrents cannot carry a net spin. Furthermore, since singlet pairs are easily disrupted by magnetism, the coupling of superconductivity and magnetism might appear impossible for applications in low power superconducting or spin-electronic (spintroncs) applications. However, during the past decade and a half a series of breakthroughs have shown that, not only can magnetism and superconductivity be made to cooperate, but at engineered superconductor/magnet interfaces new functionality can be created in which spin, charge and superconducting phase coherence work together synergistically (1-3). By combining these different degrees of freedom, a new spectrum of exciting predictions is waiting to be explored, and a new field of superspintronics has emerged.
    This introductory talk will highlight some aspects of the new field of superspintronics with a particular focus on work undertaken by my group. I will discuss, e.g., the creation of spin-polarized triplet Cooper pairs at superconductor/magnetic interfaces (1-3), spin-pumping of superconducting spin currents (4), and triplet pair interaction with spin-orbit coupling (5). I will also outline some of my groups other related work-e.g. on chiral magnetism (6) and superconducting diode effects (7). Finally, I will highlight interesting directions going forward involving two-dimensional van der Waals quantum solids.

• Title: Ab initio DMFT methodologies for correlated quantum materials

• Speaker: Prof. Choi Sangkook (School of Computational Sciences, KIAS)

• Date & Time / Venue: January 22nd (Mon.), 2024, 2:00 PM / APCTP #512, Pohang & Online via ZOOM

• ZOOM Link : https://us06web.zoom.us/meeting/register/tZYrcOqqrTksGtKuzm3hIFKlfW5gByoya8A_

• Abstract
  : Quantum information science is a surging frontier of physical science. By creating quantum states and utilizing them as quantum bits (qubits), it promises vastly improved performance over what we have achieved during the 20th century.
  Quantum materials are a class of materials of which properties can be explained by only quantum physics. When their quantum nature is due to electron-electron interaction, quantum materials give rise to a rich tableau of novel physics. These so-called correlated quantum materials can be utilized as "semiconductors" for quantum information science.
  However, understanding correlated quantum materials properties is one of the grand challenges in the field of quantum materials. Correlated quantum materials preclude simple explanations and computationally simple methods based on Landau's Fermi liquid theory, such as density functional theory.
  In this talk, I'll introduce ab initio DMFT approaches, especially LQSGW+DMFT[1,2] and full GW+EDMFT [3]. I will also show several interesting physics found in correlated quantum material including infinite-layer nickelate [4,5], Fe-based superconductors[6].

References
[1] S. Choi, P. Semon, B. Kang, A. Kutepov, and G. Kotliar, Comp. Phys. Comm. 244, 277 (2019)
[2] S. Choi, A. Kutepov, K. Haule, M. van Schilfgaarde, and G. Kotliar, npj Quantum Materials 1. 16001 (2016)
[3] B. Kang, P. Semon, C. Melnick, G. Kotliar, and S. Choi, arXiv:2310.04613.
[4] S. Ryee, P. Semon, M. J. Han, and S. Choi, Phys. Rev. Lett. 126, 206401 (2021)
[5] B. Kang, C. Melnick, P. Semon, S. Ryee, M. J. Han, G. Kotliar, and S. Choi, npj Quantum Mater. 8.1 (2023)
[6] M. Kim, S. Choi, W. H. Brito, and G. Kotliar, arXiv:2304.05002.

• Title: Advance in ultrafast science and related technology: “attosecond science and technology”

• Speaker: Prof. Kim, Dong Eon (POSTECH)

• Date & Time / Venue: December 13th (Wed.), 2023, 4:00 ~ 5:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : In the 21st century, interest is growing about the study of how quantum systems evolve, and eventually, how to induce such quantum systems to behave as desired. In this sense, we are entering a new scientific paradigm, “Control Age.” For example, scientists would like to move electrons around during chemical reaction processes that are far from equilibrium. The new era of science calls for new tools to control electron behavior in matters at the utmost time scale (femtosecond to attosecond) with atomic spatial resolution. The past two decades have witnessed the remarkable advance in the new metrology for ultrafast electron dynamics, which allows one to control material processes at electron level and study dynamics far away from equilibrium. This development was recognized by 2023 Nobel Prize in Physics. In this talk, I share the excitement, reviewing recent progress in the generation of ultrafast pulses ( single cycle pulse, attosecond pulse, zeptosecond pulses) and their characterization and real time measurement and manipulation of electron dynamics in atoms, molecules and condensed matters. I hope that this provides the audience with the new insights and perspective that these tools have provided in aspects of both fundamental science and future technology.

• Title: Application of machine learning to strongly correlated systems

• Speaker: Prof. Go, Ara (Chonnam national Univ.)

• Date & Time / Venue: December 6th (Wed.), 2023, 4:00 ~ 5:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Strongly correlated systems inherently involve numerous degrees of freedom, and attempts to solve these systems directly encounter exponential increases in computational costs. Machine learning techniques, known for their excellent performance in uncovering hidden correlations within data, offer an avenue to expand our capabilities in solving correlated systems. In this presentation, I introduce fundamental machine learning techniques and showcase their application to strongly correlated systems. Examples of machine learning-based approaches, such as estimating physical quantities that are challenging to measure based on easily measurable quantities, predicting the importance of a certain state in a Hilbert space, and bypassing repeated minimization processes, will be discussed to illustrate their effectiveness in addressing the challenges posed by strongly correlated systems.

• Title: A small quantum system strongly coupled with a thermostted bath

• Speaker: Prof. Chulan Kwon

• Date & Time / Venue: December 5th (Tue.), 2023, 5:00 PM / #512, APCTP

• Abstract
  : We investigate the thermalization of a small quantum system strongly coupled with a large bath thermostatted to another super bath. We suppose the bath to interact with the equilibrium super bath at the large boundary surrounding the bath, which makes weak coupling scheme valid. We use the Lindblad equation as the bath's dynamical map averaged over the super bath's degrees of freedom. However, we rigorously treat the interaction between the system and bath. In this sense, our approach is a hybrid strong coupling theory useful for most practical situations. The resultant dynamics couples the unitary dynamics of the system and the stochastic dynamical group of the bath. For an example, we consider a single harmonic system which interacts with a bath of photons via dipole interaction. We use the coherent state formalism with P-representation and derive a Fokker- Planck-like equation in infinite dimensions for the composite coherent state of the system and photons. We derive the marginal dynamics for the system by averaging out the bath's variables that are fast varying compared to the system's slowly varying ones. For a small interaction case, that is practical in real experiments, we solve the marginal dynamics in time and find the steady state solution. We find the steady state to be Boltzmann with corrections due to interaction, which is supposed to the effect of the Lamb shift. We investigate our results in comparison with the Redfield dynamics. In future, we will extend our study to other systems such as discrete-level systems and non-equilibrium systems with time-varying protocols.

• Title: Optoelectronic manifestation of orbital angular momentum driven by chiral hopping in trigonal Se chains

• Speaker: Prof. Jeongwoo Kim (Department of Physics, Incheon National University)

• Date & Time / Venue: December 5th (Tue.), 2023, 4:00 ~ 5:00 PM / Room 104(Auditorium), IBS POSTECH Campus Building

• Abstract
  : Chiral materials have garnered significant attention in the field of condensed matter physics. Nevertheless, the magnetic moment induced by the chiral spatial motion of electrons in helical materials, such as elemental Te and Se, remains inadequately understood. In this talk, I present the development of quantum angular momentum enforced by chirality using static and time-dependent density functional theory calculations for an elemental Se chain. Our findings reveal the emergence of an unconventional orbital texture driven by the chiral geometry, giving rise to a non-vanishing currentinduced orbital moment. By incorporating spin-orbit coupling, we demonstrate that a current-induced spin accumulation arises in the chiral chain, which fundamentally differs from the conventional Edelstein effect. Furthermore, we demonstrate the optoelectronic detection of the orbital angular momentum in the chiral Se chain using the generation of photocurrent under circularly polarized light. Our results provide a fundamental understanding of the interplay between spin and orbital degrees of freedom in chiral geometries, which paves the way for design of novel orbitronic/spintronic devices utilizing chiral materials

• Title:
  I) What if we see the world with PHYSICS eye?
  Bus seat/ NEW string theory/ Jack Sparrow, HAN SeokBong, and Physics
  II) Discovery of ‘Topotactic resistance switching RAM’

• Speaker: Prof. Chang Uk JUNG (Department of Physics, Hankuk University of Foreign Studies)

• Date & Time / Venue: November 21st (Tue.), 2023, 04:10 PM / Room 104(Auditorium), IBS POSTECH Campus Building

• Abstract
  : Han SeokBong was a renown penman that contributed to the Joseon dynasty’s diplomacy with the Ming dynasty (Chinese) during the Imjin war (Lee, 2009). After 5 years of practicing writing, Han SeokBong decided that he had mastered the skills of calligraphy and attempts to leave his practice space in the woods to join the bureaucracy. In response to SeokBong’s decision, his mother makes a proposition, saying “I will turn off the candle. If you can write in the dark as well as I cut this rice cake in the dark, I approve of your choice to join the bureaucracy this soon.”I as a physicist will prove that the contest between Seokbong and his mom was unfair! Although physics is full of profound and beautiful theories, you can use your imagination alone to apply simple theories in a profound and beautiful way. If time allows, I will add a few of my original talks that shows simple physics can show totally different world.; where to sit on a public bus, a new string theory(why a fiber string was attached to a pull of a zipper of sportswear/bag)
  I discovered ‘topotactic ReRAM in 2014 with simple but first tried strategy. Resistance switching random access memory(ReRAM) is a very promising candidate to replace conventional Si-based memory. However, non-uniformity in key switching parameters and low endurance observed for devices based on polycrystalline metal oxide thin films has been delaying a practical application. Here, a strategy to overcome the aforementioned problems is unveiled by using oxides having a brownmillerite structure such as SrFeO2.5 and SrCoO2.5. Our most recent device based on SrFeO2.5 displayed very high endurance over 10^7 cycles and high-speed switching time of 10 ns. The multivalencey nature of Fe(Dr Jekyll and Mr Hyde) ion was found be very efficient way to get speed, stability, gradual switching
  
  --HAN SeokBong, and Physics http://webzine.kps.or.kr/contents/index.php?process=ok&mode=count&id=webzine&cidx=12996
  --Topotactic ReRAM) Adv Mater (2013), 25, p3651/ Appl. Phys. Lett. (2014), 105, p063507./ACS Appl. Mater. Interfaces (2016), 8, p7902/ Nanoscale, (2017), 9, 10502/ Scientific Report , 9:1188 (2019)/ Adv. Mat. 1903391 (2019).
  --USA Patent (15/322/711) filed on 2016-12-29
  Title- Memory Device for Resistance Switching Using Materials Having a Brownmillerite Structure

• Title: Spin-Orbitronics 2.0: SpintronicsMeets Orbitronics (Part 1 and 2)

• Speaker: Dr. Dongwook Go (Peter Grünberg Institute and Institute for Advanced Simulation, Forschungszentrum Jülich, Germany)

• Date & Time / Venue: 

[Seminar 1] : Nov. 15th (Wed.), 13:30 ~/ Seminar Room (Bldg.3, #302) 

[Seminar 2] : Nov. 16th (Thu.), 13:30 ~ / Conference Room (Bldg.3, #101)

• Abstract
  : The electron inside a material possesses the orbital degree of freedom originating from the valence orbitals of constituent atoms, which does not exist for the electron in vacuum. However, it has been assumed that the orbital degree of freedom is “frozen” such that it cannot be easily manipulated. Nonetheless, theories predicted the existence of the flow of electrons with finite orbital angular momentum (OAM) [1], which seem to contradict the quenching of the OAM in the ground state. Despite the widespread skepticism, we showed that the orbital quenching does not necessarily prevent the dynamics and transport of OAM, which are in principle non-equilibrium phenomena, because orbitally quenched states can hybridize among each other by external perturbations [2]. The orbital currents were unambiguously confirmed by a recent magneto-optical detection experiment [3], which opens a plethora of possibilities of utilizing these new currents [4]. One of the important manifestations of orbital currents can be found in spintronics because the angular momentum can be carried by both spin and orbital degrees of freedom. For example, injection of OAM into a magnet can induce magnetic excitations [5]. So-called “orbital torque” has not only been measured from various experimental groups [6]. It turned out that many phenomena that were assumed to be due to spin currents are in fact due to orbital currents. For example, it was found that orbital currents can cause a magnetoresistance [7]. Also, the interconversion between charge and spin currents is in fact mediated by orbital currents, and harnessing the orbital-to-spin conversion can substantially enhance the efficiency of current-control of magnetization [8].

In this presentation consisting of two parts, I share the vision of orbitronics and how it can significantly reshape the landscape of spintronics research. I propose the initiative “spin-orbitronics 2.0” which aims to fully harness the potential of all charge, spin, and orbital currents and their interconversions. In the first part, I will provide an overview of the state-of-the-art of theoretical and experimental progress made so far and discuss future challenges and big questions to be answered, such as how fast orbital currents are [9], how far they propagate [10], and what their reciprocal processes are like [11]. The second part of the presentation is aimed at experts. I will delve into theories on the description of spin-orbital coupled electrons in magnetic nanostructures. I will also explain formalisms and first-principles methods, which we have developed in the past years, and how they can shed light on the profound nature of spin-orbital coupled transport and guide experiments.

[1] B. A. Bernevig et al. PRL 95, 066601 (2005); H. Kontani et al. PRL 102, 016601 (2009)

[2] D. Go, H.-W. Lee et al. PRL 121, 086602 (2018).

[3] Y. G. Choi, D. Go, H.-W. Lee, G.-M. Choi et al. Nature 619, 52 (2023).

[4] D. Go et al. EPL 135, 37001 (2021); D. Das, Nature Physics 19, 1085 (2023); T. G. Rappoport, Nature 619, 38 (2023).

[5] D. Go and H.-W. Lee, PR Research 2, 013177 (2020).

[6] D. Lee, D. Go, K.-J. Lee et al. NatCommun 12, 6710 (2021); J. Kim. D. Go, Y. Otani et al. PRB 103, L020407 (2021); H. Hayashi, D. Go. K. Ando et al. CommunPhys 6, 32 (2023); G. Sala, P. Gambardella, PR Research 4, 033037 (2022); R. Fukunaga, K. Ando et al. PR Research 5, 023054 (2023).

[7] S. Ding, D. Go, M. Kläui et al. PRL 128, 067201 (2022); S. Ding, P. Gambardella et al. PR Research 4, L032401 (2022).

[8] S. Ding, D. Go, M. Kläui et al. PRL 125, 177201 (2020); S. Lee, D. Go, B.-G. Park et al. CommunPhys 4, 234 (2021)

[9] T. S. Seifert, D. Go, T. Kampfrath et al. Nature Nanotechnology (2023); Y. Xu, A. Fert, W. Zhao et al. arXiv:2208.01866.

[10] D. Go et al. PRL 130, 246701 (2023).

[11] A. E. Hamdi, M. Viret et al. Nature Physics (2023); H. Hayashi, K. Ando, arXiv:2304.05266.

• Title: High-Tc superconductivity from an atomic point of view via tunneling

• Speaker: Prof. Lee, Jinho (SNU)

• Date & Time / Venue: November 8th (Wed.), 2023, 4:00 ~ 5:00 PM / Physics Seminar Room (Science Bldg Ⅲ, #302)

• Abstract
  : Attempts to synthesize a “room temperature superconductor” are being made all over the world, but the highest Tc at the atmospheric pressure is still about 130 K recorded in mercury-based cuprates. Even after 36 years of discovery of the high-temperature superconductivity (HTSC) from the cuprate compounds, the mechanism of the formation of Cooper pairs well above the liquid nitrogen boiling temperature is remained to be elucidated. The discovery of yet another HTSC family of iron-based superconductors seemed to add more complexity to this puzzle but also seems to render a prospect of finding a universal principle shared by the entire HTSC family. The tunneling experiments, on the other hand, also witnessed remarkable breakthroughs ever since Giaever succeeded in the first tunneling experiment on a superconducting aluminum. The scanning tunneling microscopy (STM) invented by Binnig and Rohrer began to be heavily applied to the research of condensed matter and became one of the most versatile spectroscopic tools as well as the most powerful microscope available in the HTSC research field as of today. In this talk, I would like to convey a history and a snapshot of the current application of the STM in the research of HTSC. Recent discoveries and their implications will also be discussed.

• Title: Visualization of Strongly Correlated Electrons with STM

• Speaker: Prof. Shaowei Li (University of California, San Diego)

• Date & Time / Venue: November 2nd (Thu.), 2023, 10:30 AM / Room 104(Auditorium), IBS POSTECH Campus Building

• Abstract
  : Atomically thin transition metal dichalcogenides provide an exciting new platform to design and fabricate novel electronic and optical devices. Through the precise control of the stacking order and the twist angle between two adjacent layers, the moiré superlattice can lead to tunable narrow electronic minibands, where long-range Coulomb interactions play a critical role in determining strongly correlated electron states. This has led to the observation of the Mott insulating state at half filling, as well as the generalized Wigner crystal states at fractional fillings. However, the direct microscopic understanding of these emerging quantum phases has long been hindered by many experimental challenges. In this talk, I will present a series of technical advancements in scanning tunneling microscopy which allow us to directly visualize the correlated phases in the closely aligned WS2/WSe2 moiré superlattices

• Title: Scanning Probe Microscopy on Correlated Phases in Twisted Moiré Materials

• Speaker: Prof. Oh, Myungchul (POSTECH)

• Date & Time / Venue: September 21th (Thu.), 2023, 3:00 PM / Room 105(Conference Room), IBS POSTECH Campus Building

• Abstract
  : In a flat band system, interactions between electrons become dominent due to the suppressed kinetic energy and many-body effect begins to occur. The recent breakthrough in engineering the band structure by creating a moiré superlattice in a twisted two-dimensional system has paved the way for the exploration of numerous strongly correlated quantum phenomena that emerge from the symmetry broken many-body ground state, such as correlated insulators, non-trivial topological phases, and unconventional superconductors [1-3]. In this talk, I will discuss the moiré superlattice flat band engineering in twisted two-dimensional van der Waals heterostructure and the correlated phases in the moiré superlattice systems, and describe underlying many-body physics in those phases. I will also highlight the novel scanning tunneling microscopy technique that has enhanced our understanding of the microscopic electronic structures of their ground states [1,3,4], describing details of the technical intricacies of the advanced STM instrumentation which facilitates the exploration of two-dimensional quantum material devices. keywords : many-body physics, correlated phases, twisted materials, STM References 

[1] Wong, D.*, Nuckolls, K. P.*, Oh, M.*, Lian, B.*, Xie, Y., Jeon, S., Watanabe, K., Taniguchi, T., Bernevig, B. A. & Yazdani, A. Cascade of electronic transitions in magic-angle twisted bilayer graphene. Nature 582, 198–202 (2020). 

[2] Nuckolls, K. P.*, Oh, M.*, Wong, D.*, Lian, B.*, Watanabe, K., Taniguchi, T., Bernevig, B. A. & Yazdani, A. Strongly correlated Chern insulators in magic-angle twisted bilayer graphene. Nature 588, 610–615 (2020). 

[3] Oh, M.*, Nuckolls, K. P.*, Wong, D.*, Lee, R. L., Liu, X., Watanabe, K., Taniguchi, T. & Yazdani, A. Evidence for unconventional superconductivity in twisted bilayer graphene. Nature 600, 240–245 (2021) 

[4] Nuckolls, K. P.*, Lee, R. L.*, Oh, M.*, Wong, D.*, Soejima T.*, Hong, J. P., Călugăru, D., Arbeitman, J. H., Bernevig, B. A., Watanabe, K., Taniguchi, T., Regnault, N., Zaletel M. P. , Yazdani, A. Nature 620, 525-532 (2023) 

[5] Wong, D.*, Jeon, S.*, Nuckolls, K.P.*, Oh, M.*, Kingsley, S., Yazdani, A. Rev. Sci. Instrum. 91, 023703 (2020) * These authors are equally contributed

• Title: First-principles-based study of correlated transition-metal dichalcogenides

• Speaker: Prof. Mung Joon Han (KAIST)

• Date & Time / Venue: September 26th (Tue.), 2023, 4:30 PM / Room 104(Auditorium), IBS POSTECH Campus Building

• Abstract
  : In this talk, I will present our recent efforts of understanding the correlated electron physics in transition-metal dichalcogenides. By combining conventional density functional theory (DFT) with an appropriate form of many-body techniques, we try to investigate some key aspects that can be hardly accessible solely from experiments. Through its practical total energy formulation, the standard spin-polarized DFT method enables us to make extensive material simulation and direct comparison with experiments. Based on our recent calculation results of VTe2, I will discuss the role of ‘hidden’ magnetic order coupled with charge density wave (CDW) [1, 2]. In the case of VSe2, we adopted the standard formulation of so-called DFT+DMFT (dynamical mean-field theory) to describe the phase competition between CDW and ferromagnetic order. With the aid of this unbiased temperature-dependent calculation, we were able to estimate the magnetic order parameter and found that the ferromagnetic order can stabilize without CDW deformations [3]. Finally, I will introduce the concept of GW+ extended DMFT. We used this elaborate computation scheme to understand the gap formation of TaS2. Our calculation result indicates Mott gap is well developed in the realistic parameter regime [4]. I will try to discuss difficulties as well as differences when this series of methods is applied to real material issues. References [1] Won, Kiem et al., Adv. Mater. 32 1906578 (2020) [2] Kiem et al., Nanoscale 14 10009 (2022) [3] Kim et al., 2D Materials 5 035023 (2020) [4] Kim et al., iScience 26 106681 (2023)

• Title: Stress control molecular dynamics simulation methods and applications to soft matter

• Speaker: Dr. Keiko M. Aoki

• Date & Time / Venue: September 20th (Wed.), 2023, 11:00 AM / #512, APCTP & Online via ZOOM

• ZOOM Link : https://us06web.zoom.us/meeting/register/tZclfuisrDwsHtirj0qaoHUxxNs_V47X7_V1

• Abstract
  : Stress control molecular dynamics (MD) simulation methods guarantee the system to be under hydrostatic pressure (or other conditions) even in non-equilibrium processes. Time evolution under constant surface tension can be investigated by one of the stress control methods as well. This is in contrast to conventional MD methods where only ensemble averages can be controlled. The method is effective to investigate self-organization of soft matter, as well as glassy metastable states. Discovery of a novel liquid crystal phase by the stress control method will be discussed.

• Title: European XFEL– Opportunities and Challenges (not only) for Sample Delivery

• Speaker: Dr. Joachim Schultz (European XFEL SEC group leader)

• Date & Time / Venue: October 5th (Thu.), 2023, 3:30 PM / Physics Seminar Room (Science Bldg. III, #302)

• Abstract
  : The European XFEL is an X-ray Free-Electron Laser (XFEL) user facility with unique properties. It can produce up to 2700 femtosecond short X-ray pulses per second in the photon energy range between 400 eV and 25 keV. The pulses are generated in 600 µs long trains with up to 4.5 MHz repetition rate within the trains. Ten of these pulse trains are generated per second and can be delivered flexibly to seven different instruments. The scientific instruments are optimized for a wide range of experiments in Chemistry, Physics, Material Science and Biology. In this talk we’ll give an overview of the European XFEL and the seven Instruments. Scientific opportunities and technical challenges from the unique pulse structure will be in focus of the presentation. The Sample Environment and Characterization (SEC) group at the European XFEL provides state of the art sample characterization and delivery methods for a wide area of science and operates the user laboratories. An overview of the SEC activities and the connection to the scientific instruments will be given.