A. Homer

A new network model for the integer quantum Hall effect

Abstract A Landauer–Buttiker-type formulation of backscattering between pairs of opposite directed channels is used to describe the coupling at the nodes of a network. Physically, these nodes correspond to saddle points of a slowly varying lateral potential modulation in a 2D electron system in the high magnetic field regime. We show that the network can be solved without needing a transfer matrix as used by Chalker and Coddington. We use an exponential dependence of the coupling on the filling factor of the associated Landau level. We demonstrate that our network representation allows a quantitative modeling of almost every realistic sample geometry in the quantum Hall regime, including the effect of gate electrodes across a Hall bar.

A network model for the Hall insulator

A Landauer-Buttiker type back scattering between pairs of opposite directed channels is used to describe the node of a network at the saddle point of a slowly varying potential in the high magnetic field regime. We show that the network can be solved without needing a transfer matrix like used by e.g. Chalker and Coddington.

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.

Auger recombination dynamics of lead salts under ps free electron laser excitation

Pump-probe transmission experiments have been performed on PbSe above the fundamental absorption edge near 4 μm in the temperature range 30 to 300 K, using the Dutch ps free-electron laser. For temperatures below 200 K and carrier densities above the threshold for stimulated emission, stimulated recombination represents the most efficient recombination mechanism with relatively fast kinetics in the 50–100-ps regime, in good agreement with earlier reports of photoluminescent emission. Above this temperature Auger recombination dominates, and the Auger coefficient C is determined from the pump-probe decay curves. In the low-temperature regime the Auger coefficient is determined from the decay curves at times beyond 100 ps. The Auger coefficient is approximately constant (with a value of about 8×10 -28 u2002cm 6 s -1 ) between 300 and 70 K, and then drops a value of about 1×10 -28 u2002cm 6 s -1 at 30 K, in good agreement with the theory for nonparabolic near-mirror bands and nondegenerate statistics. It is found that C for PbSe is between one and two orders of magnitude lower than for Hg 1-x Cd x Te of comparable band gap.

Magnetic field induced metal-to-insulator transition in wide quantum wells

Abstract We present a systematic experimental study of the magnetic field induced metal–insulator transition in high mobility quasi-3D wide quantum wells. Depending on carrier density and carrier mobility we observe both a metal-like and insulator-like temperature dependence as well as a magnetic field induced transition between both regimes.

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.

Landau-level lifetimes in PbTe nipi superlattices, PbTe/PbEuTe and InAs/AlSb quantum wells

Landau-level lifetimes are determined from saturation cyclotron resonance (CR) in wide parabolic wells, quantum wells and bulk PbTe-Pb1-xEuxTe systems. These narrow gap structures exhibit strong band non-parabolicity necessary to terminate the normally equi-spaced Landau-level ladder. It was not possible to saturate the bulk sample, but short lifetimes, of between 1.5 and 8 ps, were obtained for the wide parabolic well and the quantum well, respectively, utilising a multi-level rate equation model. We also report the first pump-probe cyclotron resonance result in an InAs-AlSb quantum structure. The pump-probe experiment provides a direct determination of the lifetime, giving tau = 40 ps in this InAs-AlSb sample. This shows good agreement with an 8 x 8k.p calculation