Correlated Mott insulators in a strong electric field: The effects of phonon renormalization

TL;DR

This study investigates how a Mott insulator responds to a static electric field, considering phonon effects and dissipation, revealing how phonon interactions influence steady-state current and spectral properties.

Contribution

The paper extends previous analysis by incorporating phonon self-consistency within the nonequilibrium DMFT framework, highlighting phonon effects on current suppression and temperature dependence in Mott insulators.

Findings

Self-consistent phonon treatment suppresses current at the metallic transition with optical phonons.

Optical phonons' effects are largely temperature-independent due to high phonon frequency.

Acoustic phonons cause slight current suppression near half-gap fields, with some temperature dependence.

Abstract

We characterize the response of a Mott insulating system to a static electric field in terms of its conducting and spectral properties. Dissipation is included by a coupling to fermionic baths and to either optical or acoustic phonons. This paper extends and completes the analysis made in a previous work by the authors [arXiv:2207.01921]. In the present work phonons are included diagrammatically within the Migdal approximation by also including self-consistency from the electronic feedback. The nonequilibrium steady-state is addressed by means of the dynamical mean-field theory based on the nonequilibrium Green's function approach, while the so-called auxiliary master equation approach is employed as impurity solver. With optical phonons the self-consistency suppresses the steady-state current at the onset of the metallic phase with respect to the nonself-consistent case. This is due to the interaction of phonons with the hot electrons of the lattice which increases their temperature, thus providing a less effective relaxation channel for the current-induced Joule heat. In addition, in the case of optical phonons the results are essentially independent of the temperature of the fermionic baths, as the latter is sensibly smaller than their characteristic frequency. On the other hand, with acoustic phonons the steady-state current is slightly suppressed by the self-consistent treatment only at field strengths close to half of the gap, away from the metallic phase, and especially at very small phonon frequency. Also, in this case the results seem to slightly depend on the temperature of the fermionic baths.