arXiv subjects

Gautham Vijayan

Publications and source records attributed to Gautham Vijayan.

3 recordsLinked to original sources

arXiv2026

Twist as a Mechanical Switch for Reconfigurable Stacking in h-BN

Twistronics of layered materials has emerged as a highly active field due to its profound implications for quantum electronics and materials engineering. However, the controllable manipulation of interlayer stacking remains a significant experimental challenge. Here, the homogeneous contact between hexagonal boron nitride layers is shown to be reproducibly switched between two distinct stable stacking configurations via an externally applied torque. Combining experiments and computational modelling, we identify the stacking order of these stable states as the commensurate AA and AB modes. These two states are associated with different rotational torque maxima, exhibiting an asymmetry ratio of 0.7, and distinct dynamics as a function of the twist angle. Moreover, the peak torque values scale linearly with contact area, highlighting the dominant role of edge elasticity in the twisting process. Given that the AA and AB stacking modes correspond to different out-of-plane electric polarization states, our findings offer a pathway for reconfigurable nano- and micro-electromechanical devices.

cond-mat.mes-hall↗

arXiv2025

High pressure lattice dynamics study of few layer-$\alpha$-In$_2$Se$_3$

Few-layer $\alpha$-In$_2$Se$_3$ has been studied under pressure using Raman spectroscopy in a diamond anvil cell up to 60 GPa (at room temperature). A combination of AFM and Raman was used to estimate the thickness of the specimens. While few-layer $\alpha$-In$_2$Se$_3$ shows identical structural evolution with the one of the bulk powder-like form of $\alpha$-In$_2$Se$_3$ ( $\alpha$ $\rightarrow$ $\beta^{'}$ $\rightarrow$ IV ), an abrupt $\beta^{'}$ $\rightarrow$ IV phase transition (at 45 GPa) was observed, in contrast with the case of the bulk specimen where the two phases coexist over a wide pressure range. This is attributed to the difference in specimens morphology, $i.e.$ single crystal and powder in the case of few-layer and bulk $\alpha$-In$_2$Se$_3$, respectively. This study documents the significance of specimens morphology on the observed pressure-induced phase transitions. The methodology developed in this study for performing high-pressure Raman measurements can be applied to other nanodimensional layered materials.

cond-mat.mtrl-sci↗

arXiv2024

Superlubric Brownian Motor

Brownian motors are nanoscale machines that utilize asymmetric physical interactions to generate directed motion in space. The operation mechanism relies on the random motion of nanoscale elements generated by thermal activation. On the other hand, structural superlubricity (SSL) refers to a state of nearly vanishing friction due to structural mismatch between sliding interfaces. Van-der-Waals layered materials, such as graphene are of particular interest in this regard as they exhibit atomically flat surfaces and weak interlayer interaction. In particular, the sliding barrier in these systems turned out to be extremely sensitive to temperature, leading to the observation of thermal lubrication at elevated temperatures. Herein, the unique combination of a carefully designed tilted periodic potential landscape and virtually zero friction in incommensurate 2D layered systems are used to realize a mesoscopic superlubric Brownian machine. In particular, we perform mechanical shearing of superlubric graphite contacts to examine the influence of velocity on friction and adhesion. Our results show that while friction is virtually independent of velocity below 2500 nm*sec-1, the conservative adhesion force increases by ~ 10 % with respect to the lowest measured velocity. Intriguingly, a greater amount of energy can be collected by the system once the retraction velocity is set above the protraction velocity. Our numerical calculations based on force field modelling indicate that a slow adiabatic sliding allows to utilize the available thermal energy to reduce the adhesion in agreement with our experimental observations. As a result, we demonstrate a mesoscale Brownian motor that can harvest thermal energy by adjusting the forward and backward sliding velocities and can pave the way for macroscale directed motion and energy harvesting.

cond-mat.mes-hall↗