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In this talk, we demonstrate the intriguing properties of three distinct materials: Sr2FeMoO6 thin films, tungsten (W)-doped Sr2FeMoO6 thin films, and the conducting interface of LaFeO3 and SrTiO3.
Leveraging pulsed laser deposition (PLD) as a versatile technique, we demonstrate precise control over the stoichiometry of Sr2FeMoO6 thin films, thereby achieving the highest spin-polarization within the system. Additionally, for W-doped Sr2FeMoO6 thin films, we observe fascinating transitions in both conductivity and magnetism, alongside the emergence of a substantial topological Hall effect, indicative of a non-trivial spin-texture arising from intricate ferro-antiferro interactions.
Transitioning from thin films to interfaces, we explore the crystallographic transition occurring at the LaFeO3-SrTiO3 interface, which induces a magnetic transition leading to a remarkable shift from non-spin polarized to spin-polarized conductivity. This novel phenomenon manifests as a room temperature sp...

Over the last few decades, a rapidly expanding field has dealt with emergent properties at various interfaces formed in heterostructured materials. Specifically, it has been shown that an atomically flat interface between two highly insulating oxide materials can exhibit properties not found in either of the bulk systems defining the interface, such properties covering realms of magnetic-nonmagnetic transitions, insulator-metal transitions, emergence of superconductivity, depending on specific systems and synthesis conditions.
Interestingly, there are few investigations to probe the nature of the charge carriers in such systems arising from difficulties inherent in the problem. It is generally challenging to investigate directly the nature of such interface states since these are typically buried under a depth and represent a tiny volume fraction of the entire sample.
Over the last few decades, we have established a way to extract layer-resolved electronic structure information with ...

Hall effect is one of the most studied phenomena in condensed matter physics. In its linear form, it relates the electrical potential difference perpendicular to the electrical current via a direct proportionality. Beyond the linear response regime, a recent theoretical proposal pointed to a novel form of Hall effect induced by a Berry curvature dipole, where the electric current in the nonlinear regime is always orthogonal to the local electric field and. The proposed nonlinear Hall effect unlocks an outstanding experimental challenge to properly probe, analyze, and understand the mechanism underlying transport response in the nonlinear regime. In this talk, we report a new scheme to measure and analyze nonlinear transport response from Bernal bilayer graphene. Based on angle-resolved transport measurement, we extract the nonlinear conductivity tensor and identify a non-zero component that corresponds to the nonlinear Hall effect. By examining the evolution of the conductivity tensor ...

Fractional quantum Hall (FQH) phases emerge due to strong electronic interactions and are characterized by anyonic quasiparticles, each distinguished by unique topological parameters, fractional charge, and statistics. In contrast, the integer quantum Hall (IQH) effects can be understood from the band topology of non-interacting electrons. In this talk, I will report a surprising super-universality of the critical behavior across all FQH  and IQH transitions. Contrary to the anticipated state-dependent critical exponents, our findings reveal the same critical scaling exponent $\kappa = 0.41 \pm 0.02$ and localization length exponent $\gamma = 2.4 \pm 0.2$ for fractional and integer quantum Hall transitions. From these, we extract the value of the dynamical exponent $z\approx 1$. We have achieved this in ultra-high mobility trilayer graphene devices with a metallic screening layer close to the conduction channels. The observation of these global critical exponents across various quantum...

The low-frequency fluctuations, or noise, in electrical resistance not only set a performance benchmark in devices, but also form a sensitive tool to probe non-trivial electronic phases and band structure in solids. Here we report the measurement of such noise in the electrical resistance in twisted bilayer graphene (tBLG), where the layers are misoriented close to the magic angle (θ ∼ 1 degree). At high temperatures (T >∼ 60 − 70 K), the power spectral density (PSD) of the fluctuations inside the low-energy moir ́e bands is predominantly ∝ 1/f, where f is the frequency, being generally lowest close to the magic angle, and can be well-explained within the conventional Mc. Whorter model of the ‘1/f noise’ with trap-assisted density-mobility fluctuations. At low T (

2D van der Waals materials-based heterostructures have led to new devices for fundamental science and applications. Superconducting Josephson devices based on 2D materials offer unique opportunities to engineer new functionality for quantum technology. I will present results from two classes of materials. First, proximitized graphene-based Josephson junctions lead to a quantum noise-limited parametric amplifier with performance comparable to best discrete amplifiers in this class [1]. Gate tunability of the center frequency of the amplifier, rather than flux, offers key advantages. An extension of graphene Josephson architecture to make state-of-the-art bolometers leveraging graphene's low specific heat, and I will present initial results. Second, twisted van der Waals heterostructures based on high Tc superconductor Bi2Sr2CaCu2O8+δ lead to the realization of a high-temperature Josephson diode [2] for the first time. Such Josephson diodes offer an opportunity to engineer the current ph...

Illuminating a material with light can reveal both interesting aspects of electronic and lattice degrees of freedom, as well as drive phase and topological transitions in the material itself. In this talk, I will focus on three distinct responses of a material to light: (1) Nonlinear phononic control of magnetism in bilayer CrI3, MnBi2Te4, and MnSb2Te4. (2) The non-linear photogalvanic response of Weyl semimetals with tilted cones and chiral charge up to 4 (the largest allowed in a lattice model), as well as the topological superconductor candidate 4Hb-TaS2, and (3) The coupling of phonons to electronic degrees of freedom to produce chiral phonons with large g-factors of order 1, which can be measured with Raman scattering. For nonlinear phononic control of magnetism, I will show how intense THz light can be used to transiently modify magnetic exchange constants, including their sign. In the case of the non-linear current response of Weyl systems, I will review how the quantum geometry...

Computer Engineered 2D Materials: Host for Unconventional Properties

Tanusri Saha-Dasgupta
S. N. Bose National Centre for Basic Sciences, Kolkata 700106, INDIA

In this talk, we will discuss two computer-engineered 2D materials, which are predicted to host unconventional topological properties. The first problem to discuss is robust half-metallicity and topological properties in square-net potassium manganese chalcogenides, paving the way to design topological half-metals and application possibilities in topological quantum spintronics.[1] The second problem deals with the giant Rashba effect and nonlinear anomalous Hall conductivity in a two-dimensional molybdenum-based Janus structure. With strong spin-orbit coupling and inversion symmetry broken by asymmetric surface passivation in these 2D MXene compounds, a giant Rasbha effect and a simultaneous appearance of nonlinear anomalous Hall conductivity.[2]

[1] Koushik Pradhan, Prabuddha Sanyal, and Tanusri Saha-Dasgupta, Phys. ...

Spontaneous synchronization is at the core of many natural phenomena. Your heartbeat is maintained because cells contract in a synchronous wave; some bird species synchronize their motion into flocks; quantum synchronization is responsible for laser action and superconductivity. The transition to synchrony, or between states of different patterns of synchrony, is a dynamical phase transition that has much in common with conventional phase transitions of state – for example solid to liquid, or magnetism – but the striking feature of driven dynamical systems is that the components are “active”. Consequently quantum systems with dissipation and decay are described by non-Hermitian Hamiltonians, and active matter can abandon Newton’s third law and have non-reciprocal interactions. This substantially changes the character of many-degree-of-freedom dynamical phase transitions between steady states and the critical phenomena in their vicinity, since the critical point is an “exceptional point...

Inspired by the observation of crystallization of the vortices in the intermediate field range in a Kitaev model [Phys. Rev B 108, 165118 (2023)], we delve into obtaining different superlattice formations of the vortices and the corresponding Majorana dispersions. This gives a novel possibility of governing flat bands for Majoranas and other possible excitations that may arise in analogous settings. We find several superlattice configurations of vortices where Majorana states are weakly dispersive or even fully flat with or without a gap. The gapped flat bands have a non-zero Chern number with a higher quantum metric value (bandwidth) tunable by varying applied magnetic fields. Having satisfied the ‘vortexibility condition,’ these bands can harbor fractional Chern insulator phase of the emergent Majorana fermions if appropriate interactions are present. Interestingly, we have used the projection method and maximally localized Wannier functions algorithm to identify the localizing c...

We propose an effective Hamiltonian approach to understand a variety of partially magnetically ordered phases in a Kondo lattice. Such partial order, where only selected sites are Kondo-screened while the others develop local moments, have been observed in many heavy-fermion compounds. The proposed effective Hamiltonian retains two important features of the fundamental Kondo-lattice model: (i) formation of a Kondo singlet leading to vanishing of the local magnetic moment, and (ii) spatially correlated nature of the electronic kinetic energy. The Hamiltonian belongs to a class of coupled classical-quantum models that can be reliably studied using hybrid Monte Carlo simulations. I will try to motivate the model and demonstrate the approach for the case of a square lattice where we unveil a number of magnetic phases with partial order. I will further motivate a fully classical spin model to describe the partial magnetic order in Kondo lattices.