Microwave absorption in the magnetically-induced Wigner solid phase of a two-dimensional hole system

We report the results of microwave experiments using a technique that allows both the absorption and dispersion due to the magnetically-induced insulating phase of a 2DHS to be unambiguously identified. Between 0.2 and 4 GHz, with increasing field and decreasing temperature, the microwave electric susceptibility reveals a set of increasingly sharp resonances (Q > 30 at T = 40 mK and B = 17 T, Landau level filling factor v > 0.15). These are identified as pinned magnetophonon modes of the magnetically-induced Wigner solid which occurs for v < 1/3. Non-monotonic behaviour around v = 1/5 is described by an increase in the plasmon frequency and a decrease in the pinning frequency. (C) 1998 Elsevier Science B.V. All rights reserved.