Magnetotransport in low-density $p$-Si/SiGe heterostructures: From metal through hopping insulator to Wigner glass

We study DC and AC transport in low-density $p-$Si/SiGe heterostructures at low temperatures and in a broad domain of magnetic fields up to 18 T. Complex AC conductance is determined from simultaneous measurement of velocity and attenuation of a surface acoustic wave propagating in close vicinity of the 2D hole layer. The observed behaviors of DC and AC conductance are 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 $ u$=1) to formation of the Wigner glass in the extreme quantum limit ($Bgtrsim 14$, $T lesssim 0.8$ K).