Anomalous magnetotransport in wide quantum wells

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 Shubnikov de Haas oscillations in the same manner as known from the quantum Hall effect. The onsets of plateaux in Rxy 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 Rxx and Rxy and fulfils exactly the Onsager-Casimir relation (Rij,kl(B) = Rkl,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.Comment: postscript file including 3 figs, 5 page

Single electron magneto-conductivity of a nondegenerate 2D electron system in a quantizing magnetic field

We study transport properties of a non-degenerate two-dimensional system of non-interacting electrons in the presence of a quantizing magnetic field and a short-range disorder potential. We show that the low-frequency magnetoconductivity displays a strongly asymmetric peak at a nonzero frequency. The shape of the peak is restored from the calculated 14 spectral moments, the asymptotic form of its high-frequency tail, and the scaling behavior of the conductivity for omega -> 0. We also calculate 10 spectral moments of the cyclotron resonance absorption peak and restore the corresponding (non-singular) frequency dependence using the continuous fraction expansion. Both expansions converge rapidly with increasing number of included moments, and give numerically accurate results throughout the region of interest. We discuss the possibility of experimental observation of the predicted effects for electrons on helium.Comment: RevTeX 3.0, 14 pages, 8 eps figures included with eps

2D polarons in high magnetic fields on the surface of liquid helium films

We report on measurements proving the polaronic effect in a 2D electron system prepared on helium films covering a quartz-glass substrate. In bulk systems the measured magnetoconductivity follows the extended self-consistent Born approximation (SCBA) theory up to 20 T. On films we achieved conditions at which the calculated binding energies where larger than k(B)T and the magnetoconductivity data could be interpreted by adding the collision frequency of the electron plus its associated dimple to the collision frequency caused by gas atom scattering

The AC Hall effect for electrons on liquid helium in ultra-high magnetic fields

Current-voltage phase shift measurements are reported between electrodes situated near the rim of an array located below a charged liquid helium surface. Data are taken in magnetic fields up to 20 T at a temperature near 2 K. Under these conditions, the ultra-quantum limit is reached, where the Landau level width is larger than the electron thermal energy. Interpreting the data in terms of the AC Hall effect, or edge magnetoplasmon, suggests that the Hall resistivity deviates from its classical value for fields greater than 10 T

Quantum magnetotransport in a nondegenerate two-dimensional electron gas under extremely strong magnetic fields

The quantum magnetotransport properties of a nondegenerate two-dimensional gas of electrons interacting with helium-vapor atoms above a liquid-helium surface is studied in magnetic fields up to 20 T by the ac capacitive coupling technique. The data and the theoretical analysis performed show that in the ultraquantum limit the generalized or effective collision frequency νeff of the electrons increases faster with magnetic field than the cyclotron frequency ωc. Under extremely strong magnetic fields, where the Landau level width becomes comparable to or larger than the thermal energy, the high-cyclotron-frequency approximation ωcνeff, usually assumed in quantum transport theories, is no longer valid. The self-consistent Born-approximation theory is extended to be valid for any ratio of ωc to νeff. Then it describes the data perfectly without any adjustable parameter. The results reported here also give strong support to the universality of the linear Hall resistivity

Quantization induced decrease of the Hall effect for a non-degenerate two-dimensional electron gas in high magnetic fields

The quantum magnetotransport phenomena of surface state electrons on liquid helium interacting with helium vapour atoms are investigated under extremely strong magnetic fields up to 20 T, where the Landau level width becomes comparable to or larger than the thermal energy. The data and the theoretical analysis performed show that for a non-degenerate electron gas the cyclotron frequency to generalized collision frequency ratio, characterizing the Hall effect, attains a maximum in the quantizing magnetic field region and then decreases with increasing magnetic field to a value of the order of one in high fields. The observed effects become more pronounced at higher temperature