Asymmetry in energy versus spin transport in certain interacting, disordered systems

TL;DR

This paper investigates how energy and spin transport behave differently in disordered XXZ spin chains, revealing that energy diffusion persists more broadly than spin diffusion due to underlying conservation laws.

Contribution

It demonstrates that energy transport remains diffusive over a wide range of disorder, unlike spin transport, highlighting the asymmetry caused by conservation laws in disordered XXZ chains.

Findings

Energy transport remains diffusive at high anisotropy and various disorder levels.

Spin transport becomes subdiffusive under similar conditions.

Energy diffusion is more robust than spin diffusion across the phase space.

Abstract

We study energy transport in XXZ spin chains driven to nonequilibrium configurations by thermal reservoirs of different temperatures at the boundaries. We discuss the transition between diffusive and subdiffusive transport regimes in sectors of zero and finite magnetization at high temperature. At large anisotropies we find that diffusive energy transport prevails over a large range of disorder strengths, which is in contrast to spin transport that is subdiffusive in the same regime for weak disorder strengths. However, when finite magnetization is induced, both energy and spin currents decay as a function of system size with the same exponent. Based on this, we conclude that diffusion of energy is much more pervasive than that of magnetization in these disordered spin-1/2 systems, and occurs across a significant range of the interaction-disorder parameter phase-space; we suggest this is due to conservation laws present in the clean XXZ limit.