Talks

Magic-angle twisted bilayer graphene (MATBG) exhibits a wide variety of correlated phases, spanning from insulating to superconducting and magnetic states, favored by the flat bands. The degeneracy among closely competing ground states can be lifted by polarizing spin and valley degrees of freedom; hence, the four-fold degeneracy of the low-energy electrons has a significant impact on the underlying mechanism governing the correlated phases at different band fillings. The overall phase diagram of MATBG is remarkably sensitive to external perturbations such as carrier density, electromagnetic field, pressure, temperature, and dielectric environments. Despite this unprecedented tunability, a complete understanding of the observed phases has remained elusive. In our recent study, we conducted magneto-transport measurements on MATBG proximitized by a layer of tungsten diselenide, thereby introducing finite spin-orbit coupling into the system. Our findings unveiled an anomalous Hall effect ...

The recent advances in the 2D materials, in particular, the discovery of layered 2D magnet, have shown lot of promises in the field of low dimensional spin-based devices. More importantly, the possibility of creating heterostructure helps to incorporate multiple functionalities in the nanoscale devices as well as provides access to study interface induced physical phenomena. In this talk, I will discuss our electron transport and electron spin resonance (ESR) measurements in a 2D metallic Ferromagnet (Fe4GeTe2). The magnetization data exhibit a Ferromagnetic transition at ~270K with unusual temperature dependence compared to the conventional Ferromagnet. At ~100K, there is a spin reorientation transition (SRT) where the easy axis changes from in-plane to out of plane. Our transport data indicates that the Hall coefficient changes sign and the magnetoresistance, anomalous Hall magnitude become maximum near the SRT, providing the important role of SRT on the electron transport. The ESR d...

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...