G. Span

Anomalous magnetotransport in wide quantum wells

Abstract We present magneto transport experiments of quasi 3D PbTe wide quantum wells. A plateau-like structure in the Hall resistance is observed, which corresponds to the Subnikov de Haas oscillations in the same manner as known from the quantum Hall effect. The onsets of plateaux in R xy do not correspond to 2D filling factors but coincide with the occupation of 3D (bulk-) Landau levels. At the same time a non-local signal is observed which corresponds to the structure in R xx and R xy and fulfils exactly the Onsager-Casimir relation [ R ij , kl ( B ) = R kl , ij (− B )]. We explain the behaviour in terms of edge channel transport which is controlled by a permanent backscattering across a system of “percolative EC-loops” in the bulk region. Long range potential fluctuations with an amplitude of the order of the subband splitting are explained to play an essential role in this electron system.

Magnetotransport in wide parabolic PbTe quantum wells

The 3D and 2D behaviour of wide parabolic PbTe single quantum wells, which consist of PbTe p-n-p structures, are studied theoretically and experimentally. A simple model combines the 2D sub-band levels and the 3D Landau levels in order to calculate the density of states in a magnetic field perpendicular to the 2D plane. It is shown that at a channel width of about 300 nm, one can expect to observe 3D and 2D behaviour at the same time. Magnetotransport experiments in selectively contacted Hall bar samples are performed at temperatures down to T=50 mK, and at magnetic fields up to B = 17 T.

Conductance fluctuations in PbTe wide parabolic quantum wells

Abstract We report on conductance fluctuations which are observed in local and non-local magnetotransport experiments. Although the Hall bar samples are of macroscopic size, the amplitude of the fluctuations from the local measurements is close to e2/h. It is shown that the fluctuations have to be attributed to edge channel effects.