Magnetotransport in low-densityp−Si∕SiGeheterostructures: From metal through hopping insulator to Wigner glass

Abstract

We study dc and ac transport in low-density $p\text{\ensuremath{-}}\mathrm{Si}∕\mathrm{Si}\mathrm{Ge}$ heterostructures at low temperatures and in a broad domain of magnetic fields up to $18\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. Complex ac conductance is determined from simultaneous measurement of velocity and attenuation of a surface acoustic wave propagating in close vicinity of the two-dimensional hole layer. The observed behavior of dc and ac conductances is interpreted as an evolution from metallic conductance at $B=0$ through hopping between localized states in intermediate magnetic fields (close to the plateau of the integer quantum Hall effect corresponding to the Landau-level filling factor $\ensuremath{\nu}=1$) to formation of the Wigner glass in the extreme quantum limit ($B\ensuremath{\gtrsim}14$, $T\ensuremath{\lesssim}0.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$).