Spin Transport in Quantum Spin-Orbital Liquids

TL;DR

This paper investigates spin transport in quantum spin-orbital liquids using non-equilibrium Green's functions, revealing nonlinear behavior in the gapless phase and quantized conductance in the topologically nontrivial gapped phase.

Contribution

It provides an exact solvable model analysis of out-of-equilibrium spin transport in QSOLs, highlighting topological signatures and nonlinear effects.

Findings

Nonlinear spin current-voltage relation in the gapless phase

Quantized spin conductance of 1/2π in the chiral gapped phase

Mapping of spin transport to a free fermion problem with effective baths

Abstract

Quantum spin-orbital liquids (QSOLs) are a novel phase of matter, similar to quantum spin liquids, with quantum fluctuations in both spin and orbital degrees of freedom. We use non-equilibrium Green's function theory to study out-of-equilibrium spin transport in an exactly solvable QSOL model put forward by Yao and Lee. We find that the spin transport problem can be mapped to that of a free fermion problem with effective fermionic baths that have rapidly varying density of states. In the gapless phase, the spin current $I_s-V_s$ relation is thus highly nonlinear, while in the chiral gapped phase, the spin current conductance is quantized to be $1/2\pi$ provided that the contacts are sufficiently wide. The quantized conductance is a signature of the topological nature of the chiral gapped QSOL.