Anderson localization of spinons in a spin-1/2 antiferromagnetic Heisenberg chain

TL;DR

This paper reports the first experimental observation of Anderson localization of spinons in a spin-1/2 antiferromagnetic Heisenberg chain, using ultra-low-temperature measurements on copper benzoate, revealing localization effects at very low temperatures.

Contribution

It provides the first direct evidence of spinon Anderson localization in a magnetic system, expanding the understanding of wave interference phenomena in quasiparticles.

Findings

Spinon specific heat remains linear down to 50 mK.

Spinon thermal conductivity shows linear dependence down to 300 mK.

Thermal conductivity vanishes around 100 mK, indicating localization.

Abstract

Anderson localization is a general phenomenon of wave physics, which stems from the interference between multiple scattering paths1,2. It was originally proposed for electrons in a crystal, but later was also observed for light3-5, microwaves6, ultrasound7,8, and ultracold atoms9-12. Actually, in a crystal, besides electrons there may exist other quasiparticles such as magnons and spinons. However the search for Anderson localization of these magnetic excitations is rare so far. Here we report the first observation of spinon localization in copper benzoate, an ideal compound of spin-1/2 antiferromagnetic Heisenberg chain, by ultra-low-temperature specific heat and thermal conductivity measurements. We find that while the spinon specific heat Cs displays linear temperature dependence down to 50 mK, the spinons thermal conductivity ks only manifests the linear temperature dependence down to 300 mK. Below 300 mK, ks/T decreases rapidly and vanishes at about 100 mK, which is a clear evidence for Anderson localization. Our finding opens a new window for studying such a fundamental phenomenon in condensed matter physics.