arXiv subjects

Basudha Roy

Publications and source records attributed to Basudha Roy.

3 recordsLinked to original sources

arXiv2026

Identifying mobility edge from finite temperature spectral form factor

The spectral form factor (SFF) is a measure of energy correlations and has been widely used to identify the transition from the ergodic to the localized phase in interacting many-body quantum systems. In this work, we show that in a disordered Heisenberg spin-$\frac{1}{2}$ model, the finite temperature SFF can be used to generate a canonical phase diagram exhibiting a critical temperature $T_\mathrm{MBL}$. Using simple ideas of statistical mechanics, we obtain the critical energy density $\epsilon_\mathrm{MBL}$ dual to $T_\mathrm{MBL}$. We show that the mobility edge, numerically estimated from the spread of local perturbations and the optical conductivity, indeed coincides with $\epsilon_\mathrm{MBL}$.

cond-mat.dis-nn↗

arXiv2025

Anomalous energy correlations and spectral form factor in the nonergodic phase of the $\beta$-ensemble

The $\beta$-ensemble is a prototypical model of a single particle system on a one-dimensional disordered lattice with inhomogeneous nearest neighbor hopping. Corresponding nonergodic phase has an anomalous critical energy scale, $E_c$: correlations are present above and absent below $E_c$ as reflected in the number variance. We study the dynamical properties of the $\beta$-ensemble where the critical energy controls the characteristic timescales. In particular, the spectral form factor equilibrates at a relaxation time, $t_\mathrm{R} \equiv E_c^{-1}$, which is parametrically smaller than the Heisenberg time, $t_\mathrm{H}$, given by the inverse of the mean level spacing. Incidentally, the dimensionless relaxation time, $\tau_\mathrm{R} \equiv t_\mathrm{R}/t_\mathrm{H} \ll 1$ is equal to the Dyson index, $\beta$. We show that the energy correlations are absent within a temporal window $t_\mathrm{R} < t < t_\mathrm{H}$, which we term as the correlation void. This is in contrast to the mechanism of equilibration in a typical many-body system. We analytically explain the qualitative behavior of the number variance and the spectral form factor of the $\beta$-ensemble by a spatially local mapping to the Anderson model.

cond-mat.dis-nn↗

arXiv2025

Miniature work-to-work converter engine powered by motor protein

Designing a miniature microscale engine that can override the role of thermal fluctuations has remained elusive and is an important open challenge. Here we provide the design and theoretical framework for a unique information-based engine - a work-to-work converter - comprising a sub-micron size bead and motor protein-microtubule (MT) complex in an optical trap setup. We demonstrate how by implementing a simple motor protein state-dependent feedback protocol of the optical trap stiffness, this engine is able to harness and convert the movement of a motor protein into work output. Unlike other conventional microengines, the fidelity and performance of this engine is determined by the stochasticity of motor (un)binding characteristics. We obtain an analytical form of the work distribution function, average work output and average power output, providing quantitative predictions for engine performance which are validated by stochastic simulations. Remarkably, the average work output per cycle is at least an order of magnitude higher than the thermal fluctuations and supersedes the performance of other microscale engines realized so far.

physics.bio-ph↗