Purely linear response of the quantum Hall current to space-adiabatic perturbations

TL;DR

This paper demonstrates that in quantum Hall systems and Chern insulators, the transverse current response remains quantized and linear with respect to space-adiabatic perturbations, extending the validity of the Kubo formula beyond linear response.

Contribution

The paper provides a new proof that the Kubo formula for Hall conductivity holds beyond linear response using space-adiabatic perturbation theory, applicable to both continuum and crystalline systems.

Findings

Transverse response current is quantized up to any order in electric field strength.

Kubo formula remains valid beyond linear response regime.

Applicable to quantum Hall systems and Chern insulators.

Abstract

Using recently developed tools from space-adiabatic perturbation theory, in particular the construction of a non-equilibrium almost stationary state, we give a new proof that the Kubo formula for the Hall conductivity remains valid beyond the linear response regime. In particular, we prove that, in quantum Hall systems and Chern insulators, the transverse response current is quantized up to any order in the strength of the inducing electric field. The latter is introduced as a perturbation to a periodic, spectrally gapped equilibrium Hamiltonian by means of a linear potential; existing proofs of the exactness of Kubo formula rely instead on a time-dependent magnetic potential. The result applies to both continuum and discrete crystalline systems modelling the quantum (anomalous) Hall effect.