Microwave Resonance and Carrier-Carrier Interaction in Two-Dimensional Hole Systems at High Magnetic Field

TL;DR

This study investigates microwave resonance in high-quality two-dimensional hole systems under strong magnetic fields, revealing how carrier density influences resonance frequency and indicating the importance of interactions and disorder in the insulating phase.

Contribution

It demonstrates a clear relationship between carrier density and resonance frequency, supporting the presence of a weakly pinned Wigner crystal influenced by carrier interactions.

Findings

Resonance frequency shifts to higher values as carrier density decreases.

Resonance frequency scales as n_s^{-1/2} across samples.

Carrier interactions and disorder both crucially affect insulator dynamics.

Abstract

Microwave frequency conductivity, Re($\sigma_{xx}$), of high quality two-dimensional hole systems (2DHS) in a large perpendicular magnetic field (B) is measured with the carrier density ($n_s$) of the 2DHS controlled by a backgate bias. The high B insulating phase of the 2DHS exhibits a microwave resonance that remains well-defined, but shifts to higher peak frequency ($f_{pk}$) as $n_s$ is reduced. Over a wide range of $n_s, f_{pk} \propto n_s^{-1/2}$ is observed for the two samples we measured. The data clearly indicate that both carrier-carrier interactions and disorder are indispensable in determining the dynamics of the insulator. The $n_s$ dependence of $f_{pk}$ is consistent with a weakly pinned Wigner crystal in which domain size increases with $n_s$, due to larger carrier-carrier interaction.