Current response of nonequilibrium steady states in Landau-Zener problem: Nonequilibrium Green's function approach

Abstract

The carrier generation in insulators subjected to strong electric fields is characterized by the Landau-Zener formula for the tunneling probability with a nonperturbative exponent. Despite its long history with diverse applications and extensions, study of nonequilibrium steady states and associated current response in the presence of the generated carriers has been mainly limited to numerical simulations so far. Here, we develop a framework to calculate the nonequilibrium Green's function of generic insulating systems under a DC electric field, in the presence of a fermionic heat bath. Using asymptotic expansion techniques, we derive a semi-quantitative formula for the Green's function with nonperturbative contribution. This formalism enables us to calculate dissipative current response of the nonequilibrium steady state, which turns out to be not simply characterized by the intraband current proportional to the tunneling probability. We also apply the present formalism to noncentrosymmetric insulators, and propose nonreciprocal charge and spin transport peculiar to tunneling electrons.

Rabi Regime of Current Rectification in Solids

“…[12] (see also Ref. [24]). As we will see, and contrary to the expectations of perturbation theory, in the Rabi regime, the traditional resonant shift current contributions vanish, whereas the injection currents approach a finite limit that scales as the square root of the radiation intensity in a sharp contrast to the perturbation theory expectations.…”

“…A useful starting point to appreciate the nontrivialities of such a clean limit is to analyze the problem perturbatively in the amplitude of electric field, as commonly done in most studies (see however Ref. [12,[24][25][26][27]). Perturbation theory predicts a rectified current j, that grows as the square of the amplitude of the field, j ∝ E 2 .…”