Coexistence of two hole phases in high-quality p−GaAs/AlGaAs in the vicinity of Landau-level filling factors ν=1 and ν=(1/3)

Abstract

We focused on the transverse AC magnetoconductance of a high-mobility $p$-GaAs/AlGaAs quantum well $(p=1.2\ifmmode\times\else\texttimes\fi{}{10}^{11}{\mathrm{cm}}^{\ensuremath{-}2})$ in the vicinity of two values of the Landau-level filling factor $\ensuremath{\nu}$: $\ensuremath{\nu}=1$ (integer quantum Hall effect) and $\ensuremath{\nu}=1/3$ (fractional quantum Hall effect). The complex transverse AC conductance ${\ensuremath{\sigma}}_{xx}^{\mathrm{AC}}(\ensuremath{\omega})$ was found from simultaneous measurements of attenuation and velocity of surface acoustic waves propagating along the interface between a piezoelectric crystal and the two-dimensional hole system under investigation. We analyzed both the real and imaginary parts of the hole conductance and compared the similarities and differences between the results for filling factor 1 and filling factor 1/3. Both to the left and to the right of these values maxima of a specific shape, ``wings,'' arose in the $\ensuremath{\sigma}(\ensuremath{\nu})$ dependences at those two $\ensuremath{\nu}$. Analysis of the results of our acoustic measurements at different temperatures and surface acoustic wave frequencies allowed us to attribute these wings to the formation of collective localized states, namely, the domains of a pinned Wigner crystal, i.e., a Wigner solid. While the Wigner solid has been observed in 2D hole systems previously, we were able to detect it at the highest hole density and, therefore, the lowest hole-hole interaction reported.