Spin diffusion and spin conductivity in the 2d Hubbard model

TL;DR

This paper investigates how spin diffusion and conductivity behave in the 2D Hubbard model at finite temperatures, revealing nonmonotonic temperature dependence and differences from charge transport, with implications for cold-atom experiments.

Contribution

It provides a detailed analysis of spin transport properties in the 2D Hubbard model using the finite-temperature Lanczos method, highlighting differences from charge diffusion and effects of doping.

Findings

Spin diffusion exhibits nonmonotonic temperature dependence.

Charge liberation enhances spin transport at higher temperatures.

Model calculations do not fully match recent cold-atom measurements.

Abstract

We study the spin diffusion and spin conductivity in the square lattice Hubbard model by using the finite-temperature Lanczos method. We show that the spin diffusion behaves differently from the charge diffusion and has a nonmonotonic $T$ dependence. This is due to a progressive liberation of charges that contribute to spin transport and enhance it beyond that active at low temperature due to the Heisenberg exchange. We further show that going away from half-filling and zero magnetization increases the spin diffusion, but that the increase is insufficient to reconcile the difference between the model calculations and the recent measurements on cold-atoms.