Nonequilibrium steady states of electric-field driven Mott insulators

TL;DR

This paper investigates the nonequilibrium steady states of Mott insulators under electric fields using Floquet dynamical mean-field theory, revealing complex spectral features and tunneling processes relevant for high-harmonic generation.

Contribution

It introduces a generalized tunneling formula for current analysis and explores the crossover from tunneling to multiphoton absorption regimes in driven Mott insulators.

Findings

Identification of Wannier-Stark states and sidebands in the spectrum.

Demonstration of tunneling-induced peaks in the current.

Insights into high-harmonic generation mechanisms.

Abstract

We present a systematic study of the nonequilibrium steady states (NESS) in Mott insulators driven by DC or AC electric fields, based on the Floquet dynamical mean-field theory. The results are analyzed using a generalized tunneling formula for the current, which is reminiscent of the Meir-Wingreen formula and provides insights into the relevant physical processes. In the DC case, the spectrum of the NESSs exhibits Wannier-Stark (WS) states associated with the lower and upper Hubbard bands. In addition, there emerge WS sidebands from many-body states. Using the tunneling formula, we demonstrate that the tunneling between these WS states leads to peaks or humps in the induced DC current. In the AC case, we cover a wide parameter range of excitation frequencies and field strengths to clarify the crossover from field-induced tunneling behavior in the DC limit to nonequilibrium states dominated by multiphoton absorption in the AC limit. In the crossover regime, the single-particle spectrum is characterized by a coexistence of Floquet sidebands and WS peaks, and the current and double occupation exhibits a nontrivial dependence on the field strength. The tunneling formula works quantitatively well even in the AC case, and we use it to discuss the potential cooperation of tunneling and multi-photon processes in the crossover regime. The tunneling formula and its simplified versions also provide physical insights into the high-harmonic generation in Mott insulators.