# Noise in tunneling spin current across coupled quantum spin chains

## TL;DR

This paper investigates how spin current and noise behave in coupled quantum spin chains under temperature bias, revealing unique divergence and suppression effects linked to fermionic spin operators, with implications for spintronics measurements.

## Contribution

It provides a theoretical comparison of spin transport and noise in quantum spin chains versus magnon systems, highlighting novel divergence and suppression phenomena.

## Key findings

- Temperature bias causes zero spin current and diverging Fano factor in spin chains.
- Fermionic nature of spins suppresses spin current noise in chains.
- Divergence in Fano factor parallels fractional quantum Hall physics.

## Abstract

We theoretically study the spin current and its dc noise generated between two spin-1/2 spin chains weakly coupled at a single site in the presence of an over-population of spin excitations and a temperature elevation in one subsystem relative to the other, and compare the corresponding transport quantities across two weakly coupled magnetic insulators hosting magnons. In the spin chain scenario, we find that applying a temperature bias exclusively leads to a vanishing spin current and a concomitant divergence in the spin Fano factor, defined as the spin current noise-to-signal ratio. This divergence is shown to have an exact analogy to the physics of electron scattering between fractional quantum Hall edge states and not to arise in the magnon scenario. We also reveal a suppression in the spin current noise that exclusively arises in the spin chain scenario due to the fermion nature of the spin-1/2 operators. We discuss how the spin Fano factor may be extracted experimentally via the inverse spin Hall effect used extensively in spintronics.