Wigner glass formation in 2DHG of p-Si/SiGe by high magnetic fields

Abstract

Abstract. High-frequency ac σ ac xx = σ1 − i · σ2 and dc σ dc xx conductivities were studied on a low density (p= 8.2 · 10 10 cm −2 ) 2DHG of p-Si/Si0.92Ge0.08 heterostructures by acoustic and transport techniques respectively. In the vicinity of B=3.5 T the integer quantum Hall effect related to the filling factor ν = 1 was observed and at low temperatures the ac conductance corresponds to hopping of the holes between localized states: σ2 > σ1 > 0. The features revealed in the ultraquantum limit B>14 T at low temperatures T<0.8 K: (i) negative value of σ2; (ii) small imaginary part of the ac conductance σ1 >> |σ2|; (iii) linear frequency dependence of σ1 and σ2; (iv) independence of σ1 and σ2 on the magnetic field and temperature; (v) thresholdlike behavior of the I-V curves and (vi) its hysteresis; (vii) I-V dependence in the sub-threshold region typical for a creep in a crystal I ∼ exp(−A/V 0.3 ) indicate the formation of a pinned Wigner glass.

The superconductor-insulator transition in absence of disorder

“…In the range of parameters favouring the formation of an intermediate Bose metal plateau, therefore, the observed granular structure [20][21][22] consists of a regular intertwined Wigner crystal of charges and vortices. Since in the presence of even weak disorder, the Wigner crystal remains pinned as long as the applied electric current or voltage do not exceed a critical value [44], electric conduction is mediated exclusively by the edge modes of the topological state. The only difference with respect to the QH effect case is that the creation of a small amount of quasi-particles slightly modifies the two "magnetic fields" felt by the two flavours of excitations.…”