Microwave resonance susceptibility of a two-dimensional hole system in a weak random potential

Abstract

The electric susceptibility of a high-quality two-dimensional hole system is investigated experimentally by means of radio frequency techniques in the magnetically induced solid phase. The experiments were carried out with a heterodyne spectrometer that allows us to measure both the changes in absorption and dispersion. For frequencies between 0.2 and $4\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$ the spectrum exhibits a series of four sharp resonances identified as pinned magnetophonon modes of the Wigner solid. Anomalous behavior around the Landau level filling factor of $1∕5$ indicates bulk and shear moduli variations that are not monotonic. The sharpness of the resonances and the correlation of the pinning frequency with the threshold field measured in dc transport experiments are not in agreement with the results of earlier experiments in two-dimensional electron systems. The results presented here allow for the determination of the dominant source of disorder, and indicate that long-range order remains in the hole solid despite the presence of impurities.