Evidence for two different solid phases of two-dimensional electrons in high magnetic fields

We have observed two different rf resonances in the frequency dependent real diagonal conductivity of very high quality two-dimensional electron systems in the high magnetic field insulating phase and interpret them as coming from two different pinned electron solid phases (labeled as ``A{''} and ``B{''}). The ``A{''} resonance is observable for Landau level filling nu<2/9 {[}reentrant around the nu=1/5 fractional quantum Hall effect (FQHE)] and then crosses over to the different ``B{''} resonance which dominates at sufficiently low nu. Moreover, the ``A{''} resonance is found to show dispersion with respect to the size of the transmission line, indicating that the ``A{''} phase has a large correlation length. We suggest that quantum correlations such as those responsible for FQHE may play an important role in giving rise to such different solids.