J.C. Portal

High mobility of a three-dimensional hole gas in parabolic quantum wells grown on GaAs(311)A substrates

The transport properties of a three-dimensional hole gas were investigated in wide parabolic quantum wells grown by molecular beam epitaxy on top of GaAs(311)A substrates. The p-type doping was performed using silicon and the parabolic potential was achieved with the digital-alloy technique. Hall-effect and Shubnikov–de Haas measurements carried out at low temperature revealed that the carrier mobility was more than twice higher than the one usually obtained from similar samples grown on GaAs(100) substrates using beryllium.

Shubnikov-de Haas effect in tilted magnetic fields in wide quantum well

We study the magneto-resistance of a two-dimensional electron systems in a wide quantum well. We have considered two occupied subbands subjected to the tilted magnetic field in the regime of the magneto-inter-subband oscillations. We report on both experimental and theoretical studies of such a phenomenon and deduced information on the inter-subband energy gap in the presence of the in-plane magnetic field.

Magnetotransport in a wide parabolic well superimposed with a superlattice

The electron properties of artificially disordered superlattices embedded in a wide AlGaAs parabolic well were investigated in a strong magnetic field. We demonstrated that in the extreme quantum limit the interlayer disorder results in formation of a new correlated phase. A nearly uniform electron distribution over the superlattice wells was found in a weak magnetic field. However, a nonuniform phase with partially localized electrons, representing well-developed fractional quantum Hall effect features, was observed in high magnetic field (at the filling factor νu2009<u20091). A distinct magnetic field–induced transition separates these two phases.

Interaction corrections to the longitudinal conductivity and Hall resistivity in high mobility 2D systems with intermediate density

We have studied the quantum corrections to the longitudinal conductivity and to the Hall resistivity in a parabolic quantum well with electron density ns = 3 – 4.4 × 1011 cm−2 in the temperature range between 100 mK and 1 K as a function of gate voltage and compared our data with the theory of Zala et al.. Surprisingly, the correction to the Hall resistivity was found 10–20 times larger than theoretical predictions.

Landau level crossing and ring‐like structure in a parabolic well

We have studied the quantum Hall effect in a parabolic well with two occupied subbands. The ringlike structure is found in the density‐magnetic field phase diagram for longitudinal and Hall resistances. In addition we produce a tilt angle‐magnetic field phase diagram, which also demonstrates a set of loop‐like structures. Both phase diagrams are different from the early observations in samples with lower mobility and density.

Anomalous Hall Effect In A Two‐Dimensional Hole System

We report observation of the anomalous Hall effect in wide p‐type AlxGa1−xAs parabolic wells. The Hall resistance is described by equations Rxy = B/eps at B 3T, where ps is the hole density, B0 and A are the temperature dependent coefficients. The onset of the anomalous Hall effect is coincident with the metal‐insulator transition in strong magnetic field.