Bond disorder and breakdown of ballistic heat transport in the spin-1/2 antiferromagnetic Heisenberg chain as seen in Ca-doped SrCuO2

TL;DR

This study demonstrates that even minimal bond disorder in the S=1/2 antiferromagnetic Heisenberg chain drastically suppresses ballistic heat transport, highlighting the fragile nature of integrability in these quantum systems.

Contribution

We reveal that weak bond disorder destroys ballistic heat transport in the S=1/2 AFM Heisenberg chain, contrasting with other systems, and connect this to spinon-impurity scattering and correlation decay.

Findings

Bond disorder drastically suppresses magnetic heat conductivity.

Suppression correlates with spinon-impurity scattering length.

Results highlight the fragile integrability of the Heisenberg chain.

Abstract

We study the impact of a weak bond disorder on the spinon heat transport in the S=1/2 antiferromagnetic (AFM) Heisenberg chain material Sr_{1-x}Ca_xCuO_2. We observe a drastic suppression in the magnetic heat conductivity kappa_mag even at tiny disorder levels (i.e., Ca-doping levels), in stark contrast to previous findings for kappa_mag of S=1/2 two-dimensional square lattice and two-leg spin-ladder systems, where a similar bond disorder has no effect on kappa_mag. Hence, our results underpin the exceptional role of integrability of the S=1/2 AFM Heisenberg chain model and suggest that the bond disorder effectively destroys the ballistic nature of its heat transport. We further show that the suppression of kappa_mag is captured by an effective spinon-impurity scattering length, which exhibits the same doping dependence as the long-distance exponential decay length of the spin-spin correlation as determined by density-matrix renormalization group calculations.