Microwave photoconductivity of two-dimensional electron systems with unidirectional periodic modulation

TL;DR

This paper investigates microwave-induced photoconductivity in a 2D electron gas with a unidirectional periodic potential, revealing anisotropic negative conductivity mechanisms influenced by the potential's unidirectionality.

Contribution

It introduces a theoretical analysis of microwave photoconductivity in a 2DEG with a unidirectional potential, highlighting the dominance of the distribution function mechanism along the potential and equal contributions perpendicular to it.

Findings

Distribution function mechanism dominates along the potential direction.

Both mechanisms contribute equally in the perpendicular direction.

Unidirectionality simplifies the calculation of photoconductivities.

Abstract

Motivated by the recently discovered microwave-induced ``zero-resistance'' states in two-dimensional electron systems, we study the microwave photoconductivity of a two-dimensional electron gas (2DEG) subject to a unidirectional static periodic potential. The combination of this potential, the classically strong magnetic field, and the microwave radiation may result in an anisotropic negative conductivity of the 2DEG. Similar to the case of a smooth random potential, two mechanisms contribute to the negative photoconductivity. The displacement mechanism arises from electron transitions due to disorder-assisted microwave absorption and emission. The distribution-function mechanism arises from microwave-induced changes in the electron distribution. However, the replacement of a smooth random potential by the unidirectional one, leads to different relative strengths of the two contributions to the photoconductivity. The distribution function mechanism dominates the photoconductivity in the direction of the static potential modulation, while both mechanisms contribute equally strongly to the photoconductivity in the perpendicular direction. The unidirectionality of the static potential simplifies greatly the evaluation of the photoconductivities, which follow directly from Fermi's golden rule.