Reduction of fully screened magnetoplasmons in a laterally confined anisotropic two-dimensional electron system to an isotropic one

TL;DR

This paper shows that in the fully screened limit, plasma oscillations in anisotropic 2D electron systems can be mapped to isotropic systems through a stretching transformation, simplifying analysis of magnetoplasmons.

Contribution

It introduces a method to reduce the complex anisotropic 2D magnetoplasmon problem to an isotropic one using a stretching transformation, even with electromagnetic retardation.

Findings

Anisotropic plasma oscillations are equivalent to isotropic ones under a stretching transformation.

Electromagnetic retardation renormalizes carrier masses, similar to relativity.

Analytical solutions for eigenfrequencies in the absence of magnetic field and approximate magnetodispersion in magnetic fields.

Abstract

We investigate the properties of natural two-dimensional (2D) magnetoplasma modes in laterally confined electron systems, such as 2D materials, quantum wells, or inversion layers in semiconductors, with an elliptic Fermi surface. The conductivity of the system is considered in a dynamical anisotropic Drude model. The problem is solved in the fully screened limit, i.e., under the assumption that the distance between the two-dimensional electron system and the nearby metal gate is small compared to all other lengths in the system, including the wavelength of plasmons. Remarkably, in this limit plasma oscillations in an anisotropic 2D confined system are equivalent to plasma oscillations in an isotropic 2D electron system obtained by some stretching, even when the electromagnetic retardation is taken into account. Moreover, accounting for electromagnetic retardation leads only to a renormalization of the effective masses of carriers, somewhat like in relativity. As an example, we reduce the equations describing plasmons in a gated disk with an anisotropic two-dimensional electron gas to the equations describing oscillations in an isotropic ellipse. Without a magnetic field, we solve them analytically and find eigenfrequencies. To find a solution in a magnetic field, we expand the current of plasma oscillations in the complete set of Mathieu functions. Leaving the leading terms of the expansion, we approximately find and analyze magnetodispersion for the lowest modes.