A Quick Review of Correlated Phases in Single Crystal FeTe

Sarah Edwards

Unlike its more famous family members, FeSe and FeTe1-xSex, pure bulk FeTe is the star of many fewer papers. This is due in part to the fact that it does not superconduct under ambient conditions, despite similar signatures of nematic fluctuations as seen in FeSe and even stronger spin density wave behavior. In this journal club talk, I'll review a handful of key results from significant papers on the material, focusing on the characterization of FeTe’s proposed nematic phase and its strain-switchable antiferromagnetic ordering, which some believe is the key to unlocking its superconducting potential.

ScV6Sn6: pseudogap behavior and… something else

Jonathan DeStefano

In recent years, materials with kagome lattices have gained massive attention due to the interesting electronic dispersion that arises from the geometry of this structural motif. Of particular interest are systems with large spin-orbit coupling which can make this dispersion topologically non-trivial, and how this can interact with ordered states of matter. For example, studies of the kagome materials AV3Sb5 which host a high temperature charge density wave (CDW) and low temperature superconductivity have revealed a variety of interesting phenomena including an unconventional anomalous Hall effect. Here, I will present our recent measurements of ScV6Sn6, another kagome material with a CDW but which lacks any sign of superconductivity. I will discuss our observations consistent with the formation of a high temperature pseudogap which may arise from ordering fluctuations as seen in several high temperature superconductor families. I will also present data which provides evidence of an unusual Hall effect which we do not yet fully understand.   

Triangular Lattice at Half-Filling: The Elusive Nature of Metal-Insulator Transition and (Chiral) Spin Liquid

Yusen Ye

In this talk, we will explore the unique properties and challenges of the triangular lattice Hubbard model at half-filling, with a focus on the metal-insulator transition (MIT) and the emergence of (chiral) quantum spin liquids. We will begin by introducing the concept of MIT and the particularities of the triangular lattice. We will then delve into two experimental realizations of a second-order MIT in organic salts and transition metal dichalcogenide (TMD) moiré. We will discuss the associated density matrix renormalization group (DMRG) studies that map the quantum phase diagram of the problem, which have presented numerical evidence for the existence of (chiral) spin liquids.

Moiré physics in ultracold atoms with optical lattices

Jiayi Zhu

Moiré physics has been well studied in condensed matter system after the strong correlations and superconductivity were observed in twisted-bilayer graphene in 2018. One important application of moiré superlattices is quantum simulation of correlation and many body physics. Recently, a work on moiré superlattice formed by optical lattices in ultracold atom system came out and demonstrated superfluid to Mott insulator transition. It showed this system’s potential to be versatile and accurate quantum simulators with fine controllability in lattice trap depth and interlayer coupling strength. In this week’s CMJC, we will go through and discuss two optical moiré superlattices works as attached below:

https://www.nature.com/articles/s41586-019-1851-6

https://www.nature.com/articles/s41586-023-05695-4

Charge density waves in TMDs and Kagome metals

Heonjoon Park

Charge density waves (CDWs) and their accompanying periodic lattice distortions have been the focus of extensive research. This talk will delve into the fundamental models of CDWs based on their dimensionality. Additionally, recent experimental findings regarding CDW signatures in transition metal dichalcogenides (TMDs) will be explored, as well as their potential origins. Kagome metals, another compound that exhibits unconventional CDWs, have also garnered significant attention and will be compared in nature to TMDs. 

Itinerant Ferromagnetism and the Nagaoka Effect

Eric Anderson

Magnetically ordered phases in the Hubbard model – and particularly phases with finite doping densities – remain an open area of research.  Nagaoka ferromagnetism, in addition to being a rare rigorous proof of a magnetic ground state in the Hubbard model, provides valuable insight into the underlying mechanism behind spin order in certain regions of phase space.  In this talk, I will attempt to introduce the key concepts behind our understanding of itinerant ferromagnetism and the Nagaoka effect.  I will also discuss recent experimental and theoretical results related to Nagaoka ferromagnetism, as well as other regimes where using a Nagaoka-type picture of spin correlations may prove fruitful.  

Some useful articles for those interested:

https://arxiv.org/pdf/cond-mat/9712219.pdf

https://www.nature.com/articles/s41586-020-2051-0

Probing Magnetic Systems with X-Rays

Charles Cardot

X-ray spectroscopy is a powerful probe that can provide element specific chemical and electronic information. Naturally, there have been many applications of it to understanding magnetically active systems. In this talk I will introduce some specific examples of how it been used in place of or to supplement other experimental techniques, as well as the mechanisms behind X-ray Absorption Spectroscopy (XAS) and X-ray Magnetic Circular Dichroism (XMCD). By the end, you should have some idea of the broad potential that this technique offers, as well as a barebones understanding of the physics of x-ray spectroscopy.

Bosonic quantum fluids in quantum simulators

Jiaqi Cai

Topology, strong interaction and non-markovian in quantum system can give rise to fruitful strongly correlated, entangled or non-volatile many-body state. Recently such physics is demonstrated in controllable bosonic quantum simulators such as cavity photons, superconducting microwave photonics, exciton BECs in quantum well and exciton-polaritons leading to the realization of quantum fluids of light. Interlater excitons and Moiré excitons are also potential candidates. In this talk, we will review realizations in those systems with a highlight on superconducting qubit systems as they show most understandable features. For strongly correlated bosons, key point is to discover clever ways to engineer thermal bath, effective chemical potentials and synthetic gauge field. 

https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.85.299 

Moiré Kondo Lattices

Will Holtzmann

Symmetry breaking states in kagome metal CsV3Sb5

Zhaoyu Liu

The kagome materials attract high attention in recent condensed matter physics studies, especially the kagome metal AV3Sb5 family which holds charge density wave (CDW), anomalous Hall effect, superconductivity, and possible rotational symmetry breaking state. However, there is almost controversy in every phenomenon in this compound. I will discuss them and introduce our transport measurement to clarify the rotational symmetry-breaking state in CsV3Sb5 below the CDW phase transition.

Magnetic Topological Insulators and Probing Topological States

Jack Barlow

Since the discovery of topological phases in condensed matter systems, they have proven to be of great interest to our community and the quantum information community with the potential for topologically-protected qubits. However, the potential gap to understanding their origins and effects can be overwhelming - here, I hope to demystify some of the origins of topological states and give examples of how they manifest with a focus on magnetic TIs, as well as some methods of probing these topological states in experiment.  

Synthesis of Single Crystal Intermetallic Compounds

Jonathan DeStefano

The synthesis of single crystal intermetallic compounds is a critical step to studying and understanding the unique and diverse properties of these materials. In this talk I will discuss the basics of crystal growth including widely used techniques and common issues that arise. Several case studies of widely studied systems will also be presented to give perspective on how new materials are found. 

Heavy Fermion Quantum Criticality

Elliott Rosenberg

Quantum Spin Liquids

Eric Anderson

Quantum Spin Liquids are theoretically interesting (and experimentally challenging) systems.  They are characterized by ground states with massive entanglement, and can host non-local quasiparticle excitations.  In this talk, I will discuss some theoretical models of QSLs and how these states differ from other phases of matter, before discussing candidate systems and experimental probes.  I hope that this talk will serve as an introductory overview to QSL systems, show why they are interesting, and give some hints to the regimes in which they might be experimentally realized.

A useful review article:

https://arxiv.org/abs/1601.03742

Shape- and Fano-Feshbach-type resonances and their realizations(?) in two-dimensional semiconductor

Jiaqi Cai

We will review the theory of shape and Feshbach resonance in quantum mechanics. Several examples from quantum mechanics, superconducting resonators/qubits, and ultracold atomic gases/lattice will be given. Then we will discuss dimers and molecules in two dimensional semiconductors. We then make connection how the shape and Feshbach resonances contributes to the optical spectrum. Several bad usages of Feshbach resonances will also be discussed. 

References and Resources:

1. https://www.science.org/doi/full/10.1126/science.abj3831 [science.org]

2. https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.129.037401 [journals.aps.org]

Some additional references, with 0. a famous quantum mechanics textbook- Messiah's quantum mechanics (search resonances in the pdf. Finite well is the shape resonance and while two body collison is the Fano resonances.)

1. Feshbach resonance original paper:https://www.sciencedirect.com/science/article/pii/000349166290221X [sciencedirect.com]

2. Fano's original paper: https://journals.aps.org/pr/abstract/10.1103/PhysRev.124.1866 [journals.aps.org]

3. (possibly) the most famous paper about Feshbach resonance in atomic gases:https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.82.1225 [journals.aps.org]

4.  Feshbach resonance in semiconductor cavity-polariton system:https://www.nature.com/articles/nphys2999 [nature.com]

5. The best photoionization paper that I love for showing fano and shape resonances: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.38.228 [journals.aps.org](experiment), https://journals.aps.org/pra/pdf/10.1103/PhysRevA.14.2159 [journals.aps.org] (theory)