Quantum spin chain shows unexpected current behavior

Takato Yoshimura of King's College London, along with colleagues, has revealed that the quantum XXZ spin-1/2 chain exhibits non-Gaussian spin current fluctuations when subjected to easy-axis anisotropy. Utilizing ballistic macroscopic fluctuation theory, the researchers derived the exact probability distribution of these fluctuations in thermal equilibrium, finding it fully characterized by its variance. This work analytically connects that variance to the spin diffusion constant and static spin susceptibility, and importantly, unveils how a mechanism driving anomalous charge current fluctuations in single-file systems also manifests in the XXZ chain, establishing a universal hydrodynamic origin for these observed fluctuations. The quantum XXZ spin-1/2 chain defies expectations for macroscopic simplicity, exhibiting spin current…