Ref HAL: hal-00544453_v1
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In this paper we report on both experimental and theoretical studies of the voltage drop across the source contact in the quantum Hall effect regime at high currents. Our investigations have been performed on the plateau v = 2 using two Hall bars of different widths, processed on the same sample. A steep increase of the voltage drop across the source contact is observed experimentally well before the breakdown of the quantum Hall effect. This behaviour is analysed in the framework of inter and intra Landau level scatterings. The theoretical curves reproduce correctly the main aspects of the experimental data. Our work corroborates the results published recently by the group of Komiyama upon the Landau emission of two-dimensional electron gas.

Ref HAL: hal-03037692_v1
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We have used silicon impurities in an aluminum arsenide barrier to probe an adjacent two-dimensional electron gas (2DEG). A single impurity acts as a local spectrometer and scans the local density of states of the 2DEG. Magnetotransport experiments have been performed at low temperature with a magnetic field B applied along the direction of the current. Current-voltage characteristics strongly depend on B and reveal the formation of Landau levels (LLs).

Commentaires: 11th International Symposium on Nanostructures - Physics and Technology, St Petersburg, RUSSIA, JUN 23-28, 2003

Ref HAL: hal-03037548_v1
DOI: 10.1142/S0219581X03001656
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We present calculations of the quantum oscillations appearing in the transmission of a mesoscopic GaAs/GaAlAs ring isolated by quantum point contacts. We show that the device acts as an electronic Fabry-Perot spectrometer in the quantum Hall effect regime, and discuss the effect of the coherence length of edge states.

Commentaires: 11th International Symposium on Nanostructures - Physics and Technology, St Petersburg, RUSSIA, JUN 23-28, 2003

Ref HAL: hal-00544460_v1
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By combining exact diagonalization with scaling method, we show that it is possible to realize two-channel spin-1/2 Kondo (2CK) conductance in a quantum dot at Coulomb Blockade, with an odd number of electrons and with contacts in a pillar configuration, as an applied orthogonal magnetic field B is tuned at an appropriate level crossing.

Ref HAL: hal-00544459_v1
DOI: 10.1103/PhysRevB.65.245210
WoS: 000177043100056
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7 Citations
Résumé:

Binding energy of donors in high quality epitaxial GaAs is investigated as a function of the magnetic field between 0 and 12 T. Transverse magnetoresistance and the Hall effect are used as experimental tools. The samples are characterized using temperature dependence of free electron density and mobility, taking consistently into account the Hall scattering factor and the effective conduction depth of the structure. Our analysis of the data at the freeze-out regime of higher magnetic fields allows for the hopping conductivity over donor states. The determined magnetodonor energies are about 1 meV lower than the theoretical ones, which represents a very large improvement in comparison with previous studies.

Ref HAL: hal-00544546_v1
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We discuss a new entangled state that has been observed in the conduction across a quantum dot. At Coulomb blockade, electrons from the contacts correlate strongly to those localized in the dot, due to cotunneling processes. Because of the strong Coulomb repulsion on the dot, its electron number is unchanged w.r.to the dot in isolation, but the total spin is fully or partly compensated. In a dot with N=even at the singlet-triplet crossing, which occurs in large magnetic field, Kondo correlations lead to a total spin S=1/2.

Ref HAL: hal-00544463_v1
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The effect of an internal piezoelectric field on electrical transport phenomena has been studied in GaAlAs/GaInAs heterostructures grown on (001) and (111)B GaAs substrates. The two-dimensional electron gas (2DEG) in the structure was obtained by conventional modulation delta -doping in the barrier layer. The: conductivity and Nail effect were studied at room temperature as a function of hydrostatic pressures up to 1000 MPa. The observed pressure changes of the 2DEG concentration have been compared with theoretical predictions, taking into account the strain-induced electric fields in the barrier layer. The piezoresistive behaviour under uniaxial stress has also been determined. It was found that piezo-effects are more pronounced in the case of the material with the built-in piezoelectric field.