Chirality, causality, and fluctuation-dissipation theorems in non-equilibrium steady states

TL;DR

This paper derives fluctuation-dissipation relations specific to non-equilibrium chiral systems, linking nonlinear response and fluctuations, and providing a method to test the chiral nature of quantum systems.

Contribution

It introduces a family of fluctuation-dissipation theorems applicable to non-equilibrium steady states with chiral transport, a novel theoretical development.

Findings

Theorems connect nonlinear response with fluctuations in chiral systems

Relations hold only in systems with chiral transport

Can be used to test the chiral or non-chiral character of quantum systems

Abstract

Edges of some quantum Hall liquids and a number of other systems exhibit chiral transport: excitations can propagate in one direction only, e.g., clockwise. We derive a family of fluctuation-dissipation relations in non-equilibrium steady states of such chiral systems. The theorems connect nonlinear response with fluctuations far from thermal equilibrium and hold only in case of chiral transport. They can be used to test chiral or non-chiral character of the system.