Static and high-frequency hole transport in p -Si/SiGe heterostructures in the extreme quantum limit

Complex high-frequency (HF), σ AC = σ 1 − i σ 2 , and static, σ DC , conductivities, as well as current-voltage characteristics, have been measured in p -Si/SiGe heterostructures with a low hole density ( p = 8.2 × 10 10 cm −2 ) at temperatures T = 0.3–4.2 K in the ultraquantum limit, when the filling factor is v < 1. In order to determine the components of the HF conductivity, the acoustic contactless method in the “hybrid configuration” is used, when the surface acoustic wave propagates on the surface of the LiNbO 3 piezoelectric and the heterostructure is pressed to the surface by a spring. The conductivities σ 1 and σ 2 are determined from the damping and velocity of the surface acoustic waves that are measured simultaneously with varying the magnetic field. The revealed HF conductivity features—σ 1 ≫ |σ 2 |, the negative sign of σ 2 , the threshold behavior of the current-voltage characteristic, and the dependence I ∝ exp(- A/V 0.3 ) in the subthreshold region—indicate the formation of a pinned Wigner crystal (glass) in the ultraquantum limit ( T = 0.3–0.8 K, B > 14 T).