arXiv subjects

Chithra H. Sharma

Publications and source records attributed to Chithra H. Sharma.

8 recordsLinked to original sources

arXiv2026

Topological spin-texture transitions in van der Waals magnets revealed by X-ray Fourier transform holography

Nontrivial topological spin-textures, such as skyrmions, merons, bimerons, and skyrmioniums, are envisioned as robust building blocks for future memory and logic devices. Controllable transformations between these states require a quantum-mechanical description of electronic degrees of freedom and atomic-scale insight beyond existing phenomenological models. Here, we report an atomic-scale investigation of topological phase transitions and their protection in the two-dimensional van der Waals ferromagnet Fe$_3$GeTe$_2$ (FGT) using a combined experimental-theoretical approach. Synchrotron-based Fourier transform holography directly images labyrinth domains, isolated skyrmions, mixed labyrinth-skyrmion phases, and skyrmion bags with high spatial resolution. We compare these observations to simulations based on an electronic lattice Hamiltonian that captures both metallicity and relativistic spin-orbit coupling in FGT. By systematically exploring a broad range of temperatures and magnetic fields, we map the mechanisms governing topological transitions and their stability. This sequential-integrated experimental-theoretical framework advances understanding of spin-texture interactions and enables precise control of external tuning parameters. Our results establish a platform for creating, stabilizing, and manipulating topological states, paving the way for engineered spin-texture transitions in next-generation spintronic technologies.

cond-mat.mtrl-sci↗

arXiv2024

Resistively detected electron spin resonance and g-factor in few-layer exfoliated MoS2 devices

MoS2 has recently emerged as a promising material for enabling quantum devices and spintronic applications. In this context, an improved physical understanding of the g-factor of MoS2 depending on device geometry is of great importance. Resistively detected electron spin resonance (RD-ESR) could be employed to and the determine the g-factor in micron-scale devices However, its application and RD-ESR studies have been limited by Schottky or high-resistance contacts to MoS2. Here, we exploit naturally n-doped few-layer MoS2 devices with ohmic tin (Sn) contacts that allow the electrical study of spin phenomena. Resonant excitation of electron spins and resistive detection is a possible path to exploit the spin effects in MoS2 devices. Using RD-ESR, we determine the g-factor of few-layer MoS2 to be ~1.92 and observe that the g-factor value is independent of the charge carrier density within the limits of our measurements.

cond-mat.mes-hall↗

arXiv2023

Addressing the spin-valley flavors in moir'e mini-bands of MoS2

The physics of moir'e superlattices and the resulting formation of mini-bands in van der Waals materials have opened up an exciting new field in condensed matter physics. These systems exhibit a rich phase diagram of novel physical phenomena and exotic correlated phases that emerge in the low-dispersing bands. Transition metal dichalcogenides, in particular, molybdenum disulfide (MoS2), are potential candidates to extend the studies on moir'e electronics beyond graphene. Our transport spectroscopy measurements and analysis reveal a correlation-driven phase transition and the emergence of discrete mini-bands in MoS2 moir'e superlattices that remained elusive so far. We resolve these mini-bands arising from quantum mechanical tunneling through Schottky barriers between the MoS2 and its metallic leads. Energy scales deduced from a first approach exhibit an astounding agreement with our experimental observations. The behavior under thermal activation suggests a Lifshitz phase transition at low temperatures that is driven by a complete spin-valley symmetry breaking. These intriguing observations bring out the potential of twisted MoS2 to explore correlated electron states and associated physics.

cond-mat.mes-hall↗

arXiv2022

Acoustically Induced Giant Synthetic Hall Voltages in Graphene

Any departure from graphene's flatness leads to the emergence of artificial gauge fields that act on the motion of the Dirac fermions through an associated pseudomagnetic field. Here, we demonstrate the tunability of strong gauge fields in non-local experiments using a large planar graphene sheet that conforms to the deformation of a piezoelectric layer by a surface acoustic wave. The acoustic wave induces a longitudinal and a giant synthetic Hall voltage in the absence of external magnetic fields. The superposition of a synthetic Hall potential and a conventional Hall voltage can annihilate the sample's transversal potential at large external magnetic fields. Surface acoustic waves thus provide a promising and facile avenue for the exploit of gauge fields in large planar graphene systems.

cond-mat.mes-hall↗

arXiv2022

Electron-Spin-Resonance in a proximity-coupled MoS2/Graphene van-der-Waals heterostructure

Coupling graphene's excellent electron and spin transport properties with higher spin-orbit coupling material allows tackling the hurdle of spin manipulation in graphene, due to the proximity to van-der-Waals layers. Here we use magneto transport measurements to study the electron spin resonance on a combined system of graphene and MoS2 at 1.5K. The electron spin resonance measurements are performed in the frequency range of 18-33GHz, which allows us to determine the g-factor in the system. We measure average g-factor of 1.91 for our hybrid system which is a considerable shift compared to what is observed in graphene on SiO2. This is a clear indication of proximity induced SOC in graphene in accordance with theoretical predictions.

cond-mat.mes-hall↗

arXiv2018

2D superconductivity and vortex dynamics in 1T-MoS2

Two-dimensional (2D) superconductivity is a fascinating phenomenon packed with rich physics and wide technological application. The vortices and their dynamics arising from classical and quantum fluctuations give rise to Berezinskii-Kosterlitz-Thouless (BKT) transition and 2D Bose metallic phase both of which are of fundamental interest. In 2D, observation of superconductivity and the associated phenomena are sensitive to material disorders. Highly crystalline and inherently 2D van der Waals (vW) systems with carrier concentration and conductivity approaching metallic regime have been a potential platform. The metallic 1T phase of MoS2, a widely explored vW material system controllably, engineered from the semiconducting 2H phase, is a tangible choice. Here, we report the observation of 2D superconductivity accompanied by BKT transition and Bose metallic state in a few-layer 1T-MoS2. Structural characterization shows excellent crystallinity over extended lateral dimension. The electrical characterization confirms the metallic nature down to 4 K and a transition to a superconducting state below 1.2 K with a Tc ~ 920 mK. The 2D nature of the superconducting state is confirmed from the magneto-transport anisotropy against field orientations and the presence of BKT transition. In addition, our sample showcases a manifold increase in the parallel upper-critical-field above the Pauli limit. The inherent two-dimensionality and possibility of scalably engineering semiconducting, metallic and superconducting phases makes MoS2 a potential candidate for hosting monolithic all-two-dimensional hybrid quantum devices.

cond-mat.mes-hall↗

arXiv2018

Stable and scalable metallic phase on MoS2 using forming-gas microwave plasma

Monolithic realization of metallic 1T and semiconducting 2H polymorphic phases makes MoS2 a potential candidate for future microelectronic circuits. Though co-existence of these phases has been reported, a method for engineering a stable 1T phase in a scalable manner, compatible with the standard device fabrication schemes is yet to emerge. In addition, there are no comprehensive studies on the electrical properties of the 1T phase. In this manuscript, we demonstrate a controllable and scalable 2H to 1T phase engineering technique for MoS2 using Ar + H2 microwave plasma. The technique enables us to realize 1T MoS2 starting from the 2H phase of arbitrary thickness and area. Our method allows lithographically defining continuous 1T regions in a 2H sample. The 1T samples withstand aging in excess of a few weeks in ambience and show a thermal stability up to 300 C, making it suitable for standard device fabrication techniques. We conduct both two-probe and four-probe electrical transport measurements on devices with back-gated field effect transistor geometry in a temperature range of 4 K to 300 K. The 1T samples exhibit Ohmic current-voltage characteristics in all temperature ranges without any dependence to the gate voltage, a signature indicative of metallic state. The sheet resistance of our 1T MoS2 sample is considerably lower than that of 2H samples while the carrier concentration of the 1T sample is few orders of magnitude higher than that of the 2H samples. In addition, our samples show negligible temperature dependence of resistance from 4 K to 300 K ruling out any hoping mediated or activated electrical transport.

cond-mat.mes-hall↗

arXiv2016

Split-gate point-contact for channelizing electron transport on MoS2/h-BN hybrid structures

Electrostatically defined nanoscale devices on two-dimensional semiconductor heterostructures are the building blocks of various quantum electrical circuits. Owing to its atomically flat interfaces and the inherent two-dimensional nature, van der Waals heterostructures hold the advantage of large-scale uniformity, flexibility and portability over the conventional bulk semiconductor heterostructures. In this letter we show the operation of a split-gate defined point contact device on a MoS2/h-BN heterostructure, a first step towards realizing electrostatically gated quantum circuits on van der Waals semiconductors. Our devices show signatures of channelized electron flow and a complete shutdown of transport similar to the conventional point contacts defined on bulk semiconductor heterostructures. We explore the role of back-gate and the drain-source voltages on the pinch-off characteristics and, we are able to tune the pinch-off characteristics by varying the back-gate voltage at temperatures ranging from 4K to 300 K.

cond-mat.mes-hall↗