Title: Controlled Defect Engineering in 2D Materials by Using Ion Beam Irradiation

Abstract: Controlled defect engineering provides an effective pathway to tailor the structural, electronic, and magnetic properties of two-dimensional (2D) materials. In this work, ion beam irradiation is employed to introduce controlled defects in MoS2, WS2, hexagonal boron nitride (h-BN), highly oriented pyrolytic graphite (HOPG), and fullerene. By adjusting ion energy and fluence, vacancies, lattice distortions, and defect complexes are systematically generated within these materials. The induced defects significantly modify the electronic structure and lead to the emergence of defect-mediated magnetic ordering in otherwise non-magnetic systems. Magnetic measurements reveal that irradiation-induced vacancies and edge-like defect states play a key role in generating localized magnetic moments and enhancing magnetic response. Comparative analysis across transition metal dichalcogenides and carbon-based materials provides insight into the mechanisms responsible for defect-induced magnetism. These results demonstrate that ion beam irradiation is a versatile and controllable approach for tuning both the electronic and magnetic properties of 2D materials, with potential applications in spintronics, nanoelectronics, and advanced functional devices.

Title: Closing onto black holes

Abstract: In this talk, I will present a novel framework, the Carroll expansion, for systematically analysing the expansion of near-null surface geometries and will demonstrate that the geometry in the vicinity of a non-extremal black hole can be mapped to a specific instance of this framework called the string-Carroll expansion. I will analyse particle geodesics and scalar fields on a generic string-Carroll background and then illustrate the formalism with the example of the Schwarzschild black hole. Finally, I will demonstrate a method to reach the event horizon of the black hole from the near-horizon regime. 

Title: CHARGE-TO-SPIN CONVERSION AT SRTIO3/NIFE HETERO-INTERFACES

Abstract: The charge-to-spin interconversion at oxide interfaces has garnered significant attention from researchers due to its potential application in oxide spintronics. We have measured the charge-to-spin conversion at the perovskite STO and Ferromanget NiFe interface. Since STO in bulk is an insulator, we have deposited Oxides such as AlO or AlN, or milled the STO surface to create a conducting 2DEG layer. The charge current flows through the 2DEG layer, and the Rashba Edelstein effect at the STO interface, which locks the spin to momentum, resulting in the spin being polarised in the perpendicular direction of the charge current. We have measured the charge-to-spin conversion at the STO/Oxide/NiFe and STO(Ar+)/NiFe heterostructures. We have also found not only that this charge-to-spin conversion is unconventional [1] but also that it depends on the temperature, unlike the archetypal metallic Pt/NiFe. Our findings may enable applications of complex oxide and ferromagnet interfaces for efficient charge-to-spin conversion, paving the way for low-power oxide-based spintronic devices.

Title: Field-Free Superconducting Diode and Topological FFLO States in Altermagnetic Shiba Chains

Abstract: The superconducting diode effect (SDE), characterized by a directional asymmetry in the critical supercurrents, typically requires external magnetic fields to break time-reversal symmetry-posing challenges for device integration. Here, we demonstrate a field-free realization of the SDE in a helical Shiba chain proximitized by a d-wave altermagnet. Using a self-consistent Bogoliubov-de Gennes approach, we uncover a topological Fulde-Ferrell (FF) superconducting state hosting tunable Majorana zero modes at the chain ends. This state is stabilized by the interplay between the exchange coupling of magnetic adatoms and the induced altermagnetic spin splitting, which can be tuned by an applied supercurrent. Crucially, the same FF phase supports strong nonreciprocal supercurrents, achieving diode efficiencies exceeding 45% without applied magnetic fields. The d-wave altermagnet simultaneously breaks time-reversal and inversion symmetries via momentum-dependent spin splitting, enabling both topological superconductivity and the field-free SDE in a junction-free setting. Our findings establish Shiba chain–altermagnet heterostructures as a scalable platform for supercurrent-tunable topological superconductivity and intrinsic, field-free superconducting diodes for dissipationless quantum technologies.

The charge-to-spin interconversion at oxide interfaces has garnered significant attention from researchers due to its potential application in oxide spintronics. We have measured the charge-to-spin conversion at the perovskite STO and Ferromanget NiFe interface. Since STO in bulk is an insulator, we have deposited Oxides such as AlO or AlN, or milled the STO surface to create a conducting 2DEG layer. The charge current flows through the 2DEG layer, and the Rashba Edelstein effect at the STO interface, which locks the spin to momentum, resulting in the spin being polarised in the perpendicular direction of the charge current. We have measured the charge-to-spin conversion at the STO/Oxide/NiFe and STO(Ar+)/NiFe heterostructures. We have also found not only that this charge-to-spin conversion is unconventional [1] but also that it depends on the temperature, unlike the archetypal metallic Pt/NiFe. Our findings may enable applications of complex oxide and ferromagnet interfaces for efficient charge-to-spin conversion, paving the way for low-power oxide-based spintronic devices.

Title: Spin-torque vortex oscillators for unconventional computing applications

Abstract: As computational demands continue to rise, spintronics-based architectures are emerging as a promising platform for both neuromorphic and quantum computing applications. Within this framework, topological spin textures offer unique advantages for realizing topologically protected quantum states, providing enhanced noise immunity and thermal stability.

In this work, we demonstrate universal quantum control of magnetic vortex states, confirming their functionality as qubits for quantum computing applications. Furthermore, we have also shown magnetic vortices ability to perform real-time feature extraction and classification of multibit input patterns. This significantly reduces computation by up to 99% compared to software-based artificial neural networks (ANN), highlighting the practical potential of field-free STVOs for neuromorphic hardware and low-power computing applications

Title: Non-Bloch Band Theory in an Antiferromagnetic Spin Chain

Abstract: Understanding spin excitations in low-dimensional magnetic systems is an important problem in condensed matter physics. In this work, we study a one-dimensional antiferromagnetic spin chain with anisotropic exchange interactions, easy-axis anisotropy, and Dzyaloshinskii–Moriya interaction (DMI). An important physical realization of such models is found in van der Waals antiferromagnets, which have recently attracted significant interest. Starting from a microscopic spin Hamiltonian, we analyze the system in the regime where the ground state remains a collinear antiferromagnet. Using the Holstein–Primakoff transformation, the spin operators are mapped to bosonic excitations, allowing us to study the magnon band structure.

A central focus of this work is the application of non-Bloch band theory to understand the magnon spectrum in the presence of boundaries. Unlike the conventional Bloch description, non-Bloch theory can capture boundary-dependent features that arise in open systems. By comparing periodic and open boundary conditions, we highlight how non-Bloch ideas provide a more complete description of spin excitations in antiferromagnetic chains.
As computational demands continue to rise, spintronics-based architectures are emerging as a promising platform for both neuromorphic and quantum computing applications. Within this framework, topological spin textures offer unique advantages for realizing topologically protected quantum states, providing enhanced noise immunity and thermal stability.

In this work, we demonstrate universal quantum control of magnetic vortex states, confirming their functionality as qubits for quantum computing applications. Furthermore, we have also shown magnetic vortices ability to perform real-time feature extraction and classification of multibit input patterns. This significantly reduces computation by up to 99% compared to software-based artificial neural networks (ANN), highlighting the practical potential of field-free STVOs for neuromorphic hardware and low-power computing applications

Title: Co2C Nanoparticle-Decorated Grain Boundaries: A Source of Robust, Thermally Stable Vortex Pinning in Bi-2223 High Tc Superconductors

Abstract: In this study, we investigate the impact of cobalt carbide (Co2C) nanoparticle incorporation on the vortex pinning properties of Bi-2223 high-temperature superconductors (HTSC). Three batches of Bi-2223 pellets, containing 0%, 0.05%, and 2% by weight of Co₂C (average particle size ~ 40 nm), were analyzed. We identify two distinct Co2C pinning centers: larger inter-granular clusters (Pin-I, ~ 0.1 to 0.2 µm in size) and smaller intra-granular speckles (Pin-II, ~ 30 to 40 nm in size). By analyzing the magnetization response, we extract the behavior of the critical current density (J_c) and pinning force (F_p) as functions of field and temperature. While the δTc pinning mechanism, intrinsic to Bi-2223, was observed, our analysis also revealed additional, stronger pinning sources, which dominate at different magnetic field regimes. A Josephson-junction model showed that Co2C clusters (Pin-I) are the source of robust grain-boundary pinning at low fields, while at higher fields, collective pinning from Co2C speckles (Pin-II) becomes significant. We find the average pinning potentials due to the magnetic Co¬2C, to be, in Pin-I ~3000 meV and in Pin-II ~200 meV. Furthermore, these potentials show minimal thermal degradation, even at 77 K, thereby enhancing the pinning performance of Bi-2223 in high-temperature environments. We also estimate the range of the pinning force (L_p) due to Co2C. The strong pinning force range due to magnetic Co2C particles is estimated to remain up to a few nanometers even at temperatures as high as 80 K. The superconducting ferromagnetic properties of the Josephson junctions at Co2C-decorated grain boundaries contribute to these robust magnetic pinning features at high T. Our findings highlight the potential of transition metal carbide-HTSC nanocomposites to enhance the performance of HTSC materials, particularly in applications operating at elevated, liquid Nitrogen temperatures.

Title: Magnon driven stochastic spin Hall nano oscillators

Abstract: https://iitk-my.sharepoint.com/:w:/g/personal/guptaayush20_iitk_ac_in/IQCRYkc4f4XYR6Mj8hT-uJ3oAVHeWVRBEC1BQY4UluuubzE?rtime=evTG3amI3kg 

Title: Longitudinal Nonreciprocal Charge Transport with Time Reversal Symmetry

Abstract: Nonreciprocal charge transport enables diode-like rectification in bulk materials without conventional p–n junctions. Existing mechanisms for longitudinal nonreciprocity rely on time-reversal symmetry breaking in magnetic materials or external magnetic fields. Here, we demonstrate that longitudinal nonreciprocal charge transport can arise in nonmagnetic conductors \emph{without} magnetic

fields, purely from disorder-induced asymmetric scattering. Using a semiclassical Boltzmann framework, we develop a general theory of nonreciprocal response driven by skew scattering and side-jump processes, which remains finite even in time-reversal symmetric systems. A systematic symmetry analysis identifies the magnetic point groups that allow such extrinsic scattering–driven longitudinal nonreciprocity. As a concrete example, we show that Bernal-stacked bilayer graphene exhibits a sizable longitudinal nonreciprocity with an experimentally tunable and large nonreciprocity factor. Our results reveal a previously unexplored route to bulk rectification, motivating further exploration of disorder-driven nonreciprocity for power-efficient rectification without junction-based diodes.

Title: Instabilities and orders in a periodically-driven dissipative system

Abstract: We study order parameters and collective excitations in the periodically-driven Hubbard model coupled to a fermionic bath using the Floquet formalism. In the steady state, we obtain an expression for the mean-field gap equation in terms of the quasienergy distribution of the Floquet states. For subgap driving frequencies, we find bistability in the time-averaged order parameter, which depend on the Floquet state occupations. We consider fluctuations beyond mean-field and derive a Lindhard form for the bare polarization. The RPA susceptibility for high driving regime shows equilibrium-like low-energy magnon dispersion, and we also look at analytical expressions for the magnon distribution function. Implications are made for systems without nesting in the dispersion, but almost perfect nesting in the quasienergies. 

Title: Scaling relations of beating nodes in magnetic oscillations in graphene

Abstract: Magnetic quantum oscillations, typically periodic in the inverse magnetic field, provide a powerful probe of the geometry and topology of Fermi surfaces in metals. However, amplitude modulation of these oscillations, known as beating, can arise when multiple Fermi surface orbits of similar area coexist near the Fermi energy. In this work, we analyze the possible physical origins of beating and establish scaling relations for the carrier density at which beating nodes occur as a function of the applied magnetic field. We show that beating originating from strain-induced pseudomagnetic fields leads to a quadratic dependence of the critical carrier density on the magnetic field, whereas beating arising from valley polarization exhibits a linear scaling with the magnetic field. Importantly, these scaling relations remain robust from monolayer to multilayer graphene systems. In particular, the predicted quadratic scaling is consistent with recent experimental observation of beating in strained graphene [arXiv:2511.14888]. Our results establish beating in magnetic oscillations as a form of quantum transport spectroscopy that provides a practical route to extract key parameters such as the pseudomagnetic field strength, valley polarization, and effective spin–orbit coupling.

Title: Unconventional Computing using Magnetic Textures

Abstract: The nonlinear dynamics of droplet solitons position them as highly promising candidates for brain-inspired computing, including applications in neuromorphic systems, deep physical neural networks, physical spiking neural networks, and transformer-based physical architectures. The integration of droplet solitons into neuromorphic device architectures allows us to achieve low energy consumption while ensuring compatibility with CMOS technology. This makes them suitable for efficient hardware implementations of cognitive and perception-related tasks. However, prior research has mainly depended on the use of external magnetic fields, which present significant challenges for on-chip integration in practical computing scenarios. In this paper, we thoroughly investigate the nucleation, stability, and dynamics of droplet solitons within nanoconstriction-based spin Hall nano-oscillators (NC-SHNOs). Our approach incorporates unconventional spin-orbit torque under bias-field-free conditions, utilizing micromagnetic simulations. We illustrate stochastic spiking-like behavior in droplet solitons resulting from drift instability. This intrinsic stochastic spiking behavior can be harnessed for unconventional computing. 

Title: High order angular Hall response in multi-band semimetal

Abstract: A robust threefold modulation superimposed on the conventional cos θ angular Hall response is observed in van der Waals WTe_2 in the metallic regime at low temperatures under out-of-plane magnetic field rotation. By tuning temperature and thickness, we demonstrate that this modulation is intrinsic and originates from its near-compensated two-band electronic structure. In contrast, a few-layer graphene exhibits a richer hierarchy of higher-order angular harmonics, consistent with its multiple dynamically distinct bands. By carefully ruling out extrinsic artefacts and employing Fourier analysis, we establish angular harmonic analysis as a sensitive probe of electronic structure in multi-band semimetals. 

Title: Boundary conformal bootstrap 

Abstract: Most physical systems exist in the presence of boundaries, which cansignificantly influence their physical properties. Boundary conformal fieldtheory (BCFT) provides a useful framework for studying such systems.In BCFT, the theory is defined on a half–space with boundary conditions that preserve a subgroup of the bulk conformal symmetry. As aresult, the theory contains both bulk operators, inserted in the interior,and boundary operators that live on the boundary. The presence of theboundary leads to new structures in correlation functions and operatorproduct expansions.In this work, we study generalized free fields (GFFs) in the BCFTbootstrap framework. In particular, we consider deformations of GFFsand explore how these affect the operator spectrum and OPE data using BCFT bootstrap functionals. This work serves as a first step towardunderstanding boundary bootstrap techniques and their possible applications to interacting theories such as the critical Ising model.

Title: Emergent topological phase from a one-dimensional network of defects

Abstract: Realizing topological phases of matter in various platforms has been an intense research domain in the last decade. While developed in the context of band theory applicable to crystalline systems, topological phases have now become dominant in amorphous systems. In this context, we show that depositing impurities on one-dimensional metallic wires can lead to emergent topological phases. Such topological phases can be tuned via modulating the impurity strengths, and the emergent symmetries of the low-energy physics are different from the microscopic symmetries of the system.

We show that such phenomena can be naturally captured within a scattering network formalism where states close to the Fermi energy of the metallic wires coherently scatter via the impurities. The overall network can host both topologically trivial and non-trivial phases.

Title: Analytic study of Cosmological correlators

Abstract: Cosmological correlators encode information about the early universe but are often complicated to compute, yet they can be understood and reconstructed from simpler building blocks. Using general principles such as unitarity, their discontinuities can be expressed in terms of lower-point building blocks, and the full correlators can be rebuilt by successively cutting internal lines in the corresponding diagrams. This approach also reveals a simple connection to flat-space physics: cosmological correlators arise from standard Feynman diagrams dressed by appropriate kinematical factors.

Title: Controlling Spatial Organization of HIV Coreceptor CCR5

Abstract: CC chemokine receptor type 5 (CCR5) functions as a key coreceptor facilitating HIV entry into host cells. Recent experimental findings suggest that CCR5 preferentially localizes at lipid domain boundaries within the host cell membrane, where its positioning enhances viral fusion efficiency by allowing the HIV fusion peptide gp41 to exploit the mechanically weaker interface regions. In this study, we employ coarse-grained molecular dynamics simulations to investigate the spatial organization of CCR5 within domain forming model membranes. Our results reveal a molecular mechanism by which CCR5 preferentially migrates and stabilizes at domain boundaries. Additionally, we show that lysophosphatidylcholine (lysoPC) lipids, acting as linactants, accumulate at domain interfaces, reduce line tension, and ultimately disrupt membrane domain organization. This disruption leads to a delocalization of CCR5, potentially impairing the ability of gp41 to target membrane boundaries for fusion. Together, our findings suggest that linactants may be employed to disrupt the spatial organization of CCR5, potentially hindering HIV’s ability to initiate membrane fusion and entry.

Title: Dynamics of vacancy defects in two-dimensional entropic colloidal crystals

Abstract: Vacancy defects are observed in all ordered structures; relevant two-dimensional (2D) examples include Wigner crystals, vortices in type-II superconductors, and single-layer colloidal assemblies. These defects not only facilitate the melting of two-dimensional crystals but also determine the system's response to mechanical perturbations.

Thus, understanding the lifespan and subsequent propagation of individual defects provides valuable insights into the equilibrium and non--equilibrium properties of such systems. Although several simulation and experimental studies of the dynamics of vacancy defects exist for colloidal crystals with long-range interactions, vacancy-defect dynamics in hard-interacting, anisotropic building blocks have yet to be explored.

In this presentation, I discuss simulation and experimental studies of the dynamics of a mono-vacancy in two-dimensional entropic crystals formed by hard-interacting Brownian squares. These particles self-assemble into rhombic (RB) and hexagonal (HX) geometries at different osmotic pressures. In simulations, mono-vacancies are created by removing a particle from the lattice, whereas in experiments, they are generated by ejecting a particle using a focused laser beam. The positional fluctuations of particles surrounding the defect are tracked to analyze the underlying vacancy dynamics. Our results show that a mono-vacancy spontaneously delocalizes into multiple fractional defects that migrate along crystal axes. The collective translational motion of neighboring particles drives this process. Delocalization occurs more readily in the RB phase, where squares are side-aligned and exhibit stronger collective motion. In contrast, the random orientation of squares in the HX phase suppresses such motion, resulting in slower delocalization and longer-lived vacancies. Additionally, the three symmetry directions in the HX phase produce more isotropic vacancy dynamics compared with the two-directional symmetry of the RB phase.