arXiv subjects

Vineet Kumar Sharma

Publications and source records attributed to Vineet Kumar Sharma.

4 recordsLinked to original sources

arXiv2026

The Origin of the Observed Raman Peaks in α-MnTe

The Raman spectrum of the room-temperature altermagnet $α$-MnTe is reported to contain unassigned peaks at 120(3) cm$^{-1}$ and 140(3) cm$^{-1}$, absent from the predicted phonon spectrum of the material. This has generated considerable debate within the altermagnet community and necessitates urgent resolution. This work establishes that these peaks, together with the 90(5) cm$^{-1}$ peak that matches a theoretically predicted mode, are all extrinsic, originating from elemental tellurium formed during air exposure of the surface. Raman spectra of MBE-grown thin films show that these peaks closely match those of elemental tellurium, emerge soon after air exposure, and are absent in AlO$_x$-capped films. X-ray photoelectron spectroscopy shows that air exposure breaks Mn--Te bonds and oxidizes Mn within a minute. Cross-sectional scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy reveals that the oxidation leads to Mn out-diffusion, forming a few-nanometer-thick oxide layer above a buried, Te-enriched region, likely responsible for the anomalous Raman peaks. Additionally, no sample exhibited the 175 cm$^{-1}$ Raman peak which is commonly attributed to MnTe$_2$. The aggressive surface oxidation and associated elemental Te formation in MnTe have important implications for any surface-sensitive and optical characterization of MnTe (and other similar Te-containing materials) involving even the briefest air exposure.

cond-mat.mtrl-sci↗

arXiv2026

Engineering Nonlinear Optical Responses via Inversion Symmetry Breaking in Bilayer Bi2Se3

Paucity of naturally occurring noncentrosymmetric materials is stimulating growing interest in engineered two-dimensional systems for nonlinear optical applications. Here, we show that breaking inversion symmetry in centrosymmetric bilayer Bi$_2$Se$_3$ through twisting, point-defect insertion, or the application of an external electric field unlocks rich nonlinear optical responses. In twisted bilayer Bi$_2$Se$_3$ at the first commensurate angle of 21.78$^\circ$, we find peak shift and injection current conductivities of -14 $ nm.μAV^{-2}$ and 104 $\times 10^8$ $nm.A V^{-2}s^{-1}$, respectively, which lie in the visible spectrum and enable efficient THz applications. The external electric field and point-defect insertion both transform the bilayer into C$_ {3v}$ symmetry, with the selenium vacancy (V$_{Se}$) achieving peak shift and injection current conductivities of -190 nm.$μAV^{-2}$ and -170 $\times 10^8$ $nm.A V^{-2}s^{-1}$. In all three cases, the peak nonlinear optical responses are found to be comparable to those of benchmark 2D materials such as GeS, and the broadband responses, including helicity-dependent current generation, make these engineered bilayers viable candidates for next-generation 2D photovoltaics.

cond-mat.mtrl-sci↗

arXiv2024

Kitaev physics in the two-dimensional magnet NiPSe$_3$

The Kitaev interaction, found in candidate materials such as $α$-RuCl$_3$, occurs through the metal ($M$)-ligand ($X$)-metal ($M$) paths of the edge-sharing octahedra because the large spin-orbit coupling (SOC) on the metal atoms activates directional spin interactions. Here, we show that even in $3d$ transition-metal compounds, where the SOC of the metal atom is negligible, heavy ligands can induce bond-dependent Kitaev interactions. In this work, we take as an example the $3d$ transition-metal chalcogenophosphate NiPSe$_3$ and show that the key is found in the presence of a sizable SOC on the Se $p$ orbital, one which mediates the super-exchange between the nearest-neighbor Ni sites. Our study provides a pathway for engineering enhanced Kitaev interactions through the interplay of SOC strength, lattice distortions, and chemical substitutions.

cond-mat.str-el↗

arXiv2024

Skyrmions: A review on materials perspective for future electronic devices

Recent years have witnessed an enormous rise in research interest in magnetic skyrmions owing to their capability to improve over contemporary spintronic devices. An overview of the various magnetic interactions responsible for the formation of skyrmion together with distinct noncentrosymmetric and centrosymmetric skyrmion candidates is given in this review article. The magnetic interactions known as Dzyaloshinskii-Moriya interactions (DMI) have been extensively studied over the years to better understand the mechanism of skyrmions in chiral magnets that have larger skyrmion sizes. Because of their low skyrmion size, the centrosymmetric frustrated magnets are dwelling to skyrmions controlled by long-range interactions such as the Ruderman-Kittel-Kasuya-Yosida interaction (RKKY), which may be useful in the development of high-density memory devices. To lay a solid foundation for the magnetic interactions involved in skyrmion formations and many other special physical properties, more research in the field of centrosymmetric skyrmions is required. Apart from studying candidates with low skyrmion sizes, one of the main goals for the future is to better understand the dynamics of skyrmion using polarized magnons, which has the potential to be extremely beneficial for spintronic applications.

cond-mat.mtrl-sci↗