Static and high-frequency hole transport in p-Si/SiGe heterostructures in the extreme quantum limit
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Complex high-frequency (HF), σAC = σ1 − iσ2, and static, σDC, conductivities, as well as current-voltage characteristics, have been measured in p-Si/SiGe heterostructures with a low hole density (p = 8.2 × 1010 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 LiNbO3 piezoelectric and the heterostructure is pressed to the surface by a spring. The conductivities σ1 and σ2 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—σ1 ≫ |σ2|, the negative sign of σ2, 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).
PACS numbers73.23.-b 73.43.-f 73.50.Rb
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