Impact ionization processes in the steady state of a driven Mott insulating layer coupled to metallic leads

TL;DR

This paper investigates impact ionization in a driven Mott insulator connected to metallic leads, revealing how it significantly enhances photocurrent when the driving frequency allows impact ionization, using Floquet-DMFT methods.

Contribution

It introduces a Floquet-DMFT approach to study impact ionization effects in a driven Mott insulator coupled to leads, highlighting the role of frequency in photocurrent enhancement.

Findings

Photocurrent increases drastically when impact ionization is energetically allowed.

Suppression of current occurs at large Mott gaps where impact ionization is forbidden.

The Floquet-DMFT method with diagonal self-energy approximation is validated for this system.

Abstract

We study a simple model of photovoltaic energy harvesting across a Mott insulating gap consisting of a correlated layer connected to two metallic leads held at different chemical potentials. Upon driving the layer with a time periodic electric field a particle current is induced from the low-energy to the high-energy lead. We address in particular the issue of impact ionization, whereby a particle photoexcited to the high-energy part of the upper Hubbard band uses its extra energy to produce a second particle-hole excitation. We find a drastic increase of the photocurrent upon entering the frequency regime where impact ionization is possible. At large values of the Mott gap, where impact ionization is energetically not allowed, we observe a suppression of the current and a piling up of charge in the high-energy part of the upper Hubbard band. Our study is based on a Floquet-DMFT treatment with the so-called auxiliary master equation approach as impurity solver. We verify that an approximation, whereby the self-energy is taken diagonal in the Floquet indices, is appropriate for the parameter range we are considering.