Rabi Regime of Current Rectification in Solids

TL;DR

This paper studies rectified currents in solids under oscillating fields, revealing a Rabi regime where currents are finite and scale with the square root of intensity, bridging ideal and dissipative regimes.

Contribution

It introduces a non-perturbative framework combining Green functions and Floquet theory to describe rectification beyond perturbation theory.

Findings

Rectified current scales as the square root of radiation intensity in the Rabi regime.

Finite rectified currents are achievable in the weak coupling limit, avoiding divergence.

Provides a unified description from ideal to dissipative regimes using Floquet-Gibbs ensemble.

Abstract

We investigate rectified currents in response to oscillating electric fields in systems lacking inversion and time-reversal symmetries. These currents, in second-order perturbation theory, are inversely proportional to the relaxation rate, and, therefore, naively diverge in the ideal clean limit. Employing a combination of the non-equilibrium Green function technique and Floquet theory, we show that this is an artifact of perturbation theory, and that there is a well-defined periodic steady-state akin to Rabi oscillations leading to finite rectified currents in the limit of weak coupling to a thermal bath. In this Rabi regime the rectified current scales as the square root of the radiation intensity, in contrast with the linear scaling of the perturbative regime, allowing to readily diagnose it in experiments. More generally, our description provides a smooth interpolation from the ideal Periodic Gibbs Ensemble describing the Rabi oscillations of a closed system to the perturbative regime of rapid relaxation due to strong coupling to a thermal bath.