Electromagnetic absorption of a pinned Wigner crystal at finite temperatures

TL;DR

This paper studies microwave absorption in a pinned Wigner crystal at finite temperatures, revealing that the resonance peak remains sharp despite thermal effects, aligning with experimental data.

Contribution

It introduces a model showing the resonance peak's robustness against temperature and highlights anharmonicity as the broadening mechanism.

Findings

Resonance peak remains sharp at high temperatures.

Electron-electron interactions do not affect the response.

Anharmonicity causes broadening via self-energy corrections.

Abstract

We investigate the microwave absorption of a pinned, two-dimensional Wigner crystal in a strong magnetic field at finite temperatures. Using a model of a uniform commensurate pinning potential, we analyze thermal broadening of the electromagnetic absorption resonance. Surprisingly, we find that the pinning resonance peak should remain sharp even when the temperature is comparable or greater than the peak frequency. This result agrees qualitatively with recent experimental observations of the ac conductivity in two-dimensional hole systems in a magnetically induced insulating state. It is shown, in analogy with Kohn's theorem, that the electron-electron interaction does not affect the response of a harmonically pinned Wigner crystal to a spatially uniform external field at any temperature. We thus focus on anharmonicity in the pinning potential as a source of broadening. Using a 1/N expansion technique, we show that the broadening is introduced through the self-energy corrections to the magnetophonon Green's functions.