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Effets de spin dans les nanostructures semi-conductrices : modélisation et expériences de magnéto-transport

Abstract : The combination of spin-orbit coupling and effects associated with breakdown of inversion symmetry leads to the splitting of energy levels of real and complex band structure of bulk materials and of bidimensionnal systems such as : quantum well and heterojunction. The first part of this work consists in calculating numerically all of three contributions of spin splitting : BIA, SIA and IIA using 14-band k.p extended Kane model and new parameterization based on fits of the tight-binding band structure. Various numerical results are then compared to previous experimental results. We have obtained, for the first time, a satisfactory quantitative description of hole dispersion curves of GaAs/(AlGa)As quantum well (obtained experimentally by L. Eaves using resonant magneto-tunneling spectroscopy) and its spin splitting (reported by H. Stormer et al. some 20 years ago.). This result seems to indicate that IIA term is small in this case. We also calculated optical absorption spectra of quantum wells and obtained a good agreement with experimental result of the "quantum confined Pockels effect".

Then, we examine complex band structure of GaAs. Non-trivial exploration of complex plan is used and proves that evanescent states exist for any direction in the Brillouin zone. The complex bands emerge from extrema of the band structure in real k space and form complete loops connecting the conduction and valence bands. This result is an original contribution to the concept of spin filter.

The second part of this work reports on the experimental study of the role of spin-orbit coupling in semi-ballistic quantum wires that are obtained from a heterostructure of GaAs/(AlGa)As using electron beam lithography. We expect to observe a crossover between weak localization regime and antilocalization regime. The peaks of the magneto-resistance curve show well the weak localization regime. The analysis of weak localization curves allows to extract various characteristic times of samples and to observe the crossover between high magnetic field regime and low magnetic field regime that are associated with the nature of quasi-ballistic of the samples.
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Submitted on : Sunday, November 12, 2006 - 10:29:52 AM
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Quang Tuong Nguyen. Effets de spin dans les nanostructures semi-conductrices : modélisation et expériences de magnéto-transport. Physique [physics]. Ecole Polytechnique X, 2006. Français. ⟨tel-00113255⟩

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