Ref HAL: hal-00541607_v1
DOI: 10.1103/PhysRevB.74.245303
WoS: 000243195800065
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13 Citations
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We calculate the density of states of a two-dimensional electron gas located at the interface of a strongly disordered GaAlAs/GaAs heterojunction. The disorder potential is created by two delta doped layers. The first layer includes the parent donors which provides the well with electrons and creates a smooth disorder potential. The second layer is doped with either acceptor or donor impurities, and is located inside the well, thus creating a strongly disordered potential. We calculate the density of states in the presence of a magnetic field of arbitrary strength by taking into account all perturbative terms in the fifth Klauder's approximation. We find an anharmonic spectrum, strongly asymmetric, for the Landau level density of states. At low field, the attractive potential creates the well-known band tails or impurity bands. At higher field, we show that impurity bands are also created by repulsive potentials. We discuss the consequences of the anharmonicity and asymmetry on physical properties in the quantum Hall effect regime.

Ref HAL: hal-00166779_v1
Ref Arxiv: 0708.1448
Ref. & Cit.: NASA ADS
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Magneto-fluctuations of the normal resistance RN have been reproducibly observed in YBa2Cu3O7-d biepitaxial grain boundary junctions at low temperatures. We attribute them to mesoscopic transport in narrow channels across the grain boundary line, occurring in an unusual energy regime. The Thouless energy appears to be the relevant energy scale. Possible implications on the understanding of coherent transport of quasiparticles in HTS and of the dissipation mechanisms are discussed.

Commentaires: Submitted on behalf of EDA Publishing Association http://irevues.inist.fr/handle/2042/5920)

Ref HAL: hal-00541619_v1
DOI: 10.1002/pssa.200460439
WoS: 000228522300026
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3 Citations
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We present the analysis of magnetotransport measurements of n-type GaAs samples grown by MBE technique. The samples cover a wide range of donor concentrations, from 4.0 x 10(14) cm(-3) to 3.0 x 10(16) cm(-3). Experiments were performed for a wide range of temperatures and magnetic fields. The apparition of a magnetic freeze-out for conduction electrons allows us to extract the binding energy of donors as a function of the magnetic field as well as the impurity concentration. The measured binding energies decrease as the doping level increases. This behavior is due to the overlap of the wavefunctions of neighbouring impurities which results in the formation of an impurity band. (c) 2005 WILEY-VCH Verlag GmbH W Co. KGaA, Weinheim.

Ref HAL: hal-00541612_v1
DOI: 10.1103/PhysRevB.71.121310
WoS: 000228923300019
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16 Citations
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Far-infrared radiation absorption of a quantum dot with few electrons in an orthogonal magnetic field could monitor the crossover to the fully spin-polarized state. A Rashba spin-orbit coupling can tune the energy and the spin density of the first excited state that has a spin texture carrying one extra unit of angular momentum. The spin-orbit coupling can squeeze a flipped spin density at the center of the dot and can increase the gap in the spectrum.

Ref HAL: hal-00541611_v1
DOI: 10.1063/1.1925782
WoS: 000229544200079
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31 Citations
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Electrostatic properties of single-separated multiwalled carbon nanotubes (MWCNTs) deposited on a dielectric layer have been investigated by charge injection and electric force microscopy (EFM) experiments. We found that upon local injection from the biased EFM tip, charges delocalize over the whole nanotube length (i.e., 1-10 μ m), consistent with a capacitive charging of the MWCNT-substrate capacitance. In addition, the insulating layer supporting the nanotubes is shown to act as a charge-sensitive plate for electrons emitted from the MWCNTs at low electric fields, thus allowing the spatial mapping of MWCNT field-emission patterns. © 2005 American Institute of Physics.

Ref HAL: hal-00544451_v1
DOI: 10.1103/PhysRevB.69.045314
WoS: 000189075200059
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18 Citations
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Coulomb interactions of few (N) electrons confined in a disk-shaped quantum dot, with a large magnetic field B=B-* applied in the z direction (orthogonal to the dot), produce a fully spin-polarized ground state. We numerically study the splitting of the levels corresponding to the multiplet of total spin S=N/2 (each labeled by a different total angular momentum J(z)) in the presence of an electric field parallel to B, coupled to S by a Rashba term. We find that the first excited state is a spin exciton with a reversed spin at the origin. This is reminiscent of the quantum Hall ferromagnet at filling one, which has the skyrmionlike state as its first excited state. The spin-exciton level can be tuned with the electric field and infrared radiation can provide energy and angular momentum to excite it.

Ref HAL: hal-00544449_v1
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We present preliminary experiments on Aharonov-Bohm interferometers. We have made mesoscopic semiconductor GaAs/GaAlAs rings in which the interference phenomenon still exists in presence of a high magnetic field. This electronic interferometer is an N waves interferometer like the optical Fabry-Perot system. (C) 2004 Elsevier B.V. All rights reserved.