Photoconductivity in Ac-driven lateral superlattice in the presence of a magnetic field

TL;DR

This paper models the photoconductivity of a two-dimensional electron system in a magnetic field with a lateral superlattice under microwave irradiation, revealing strong oscillations and negative conductance states.

Contribution

It introduces a non-perturbative model incorporating Landau-Floquet states and provides a Kubo-like formula for oscillatory photoconductivity in this system.

Findings

Conductivity exhibits strong oscillations with respect to the ratio of microwave to cyclotron frequency.

Negative conductance states emerge at higher microwave power and electron mobility.

Oscillation patterns depend on multipole contributions and phase shifts.

Abstract

In this work we present a model for the photoconductivity of two-dimensional electron system in a perpendicular homogeneous magnetic field, a weak lateral superlattice, and exposed to millimeter irradiation. The model includes the microwave and Landau contributions in a non-perturbative exact way, the periodic potential is treated perturbatively. The Landau-Floquet states provide a convenient base with respect to which the lattice potential becomes time-dependent, inducing transitions between the Landau-Floquet levels. Based on this formalism, we provide a Kubo-like formula that takes into account the oscillatory Floquet structure of the problem. The total conductivity exhibits strong oscillations, determined by $\epsilon = \omega / \omega_c$ with $\omega$ the radiation frequency and $\omega_c$ the cyclotron frequency. The oscillations follow a pattern with minima centered at $\omega/\omega_c =j + {1/2} (l-1) + \delta $, and maxima centered at $\omega/\omega_c =j + {1/2} (l-1) - \delta $, where $j=1,2,3.......$, $\delta$ is a constant phase shift and $l$ is the dominant multipole contribution. Negative conductance states develop as the electron mobility and the intensity of the microwave power are increased. It is proposed that, depending on the geometry, negative conductance sates or negative resistance states may be observed in lateral superlattices fabricated in $GaAs/AlGa As$ heterostructures.