25,496 research outputs found

    Novel non-local behaviour of quasi-3D Wide Quantum Wells

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    We investigate the high magnetic field regime of wide quantum wells (WQW) for the case of a many valley host semiconductor. The complete system is described within a modified Landauer-Buettiker formalism and we demonstrate that a parallel contribution of two electron systems in different valleys of the band structure can lead to an edge channel related non-local behaviour even in the 3D-regime. From the obtained general result we derive also a simplified model which applies for the case of much different dissipation. It represents the most dissipative system by an Ohmic resistor network and the less dissipative system by an EC-system.Comment: postscript file including 3 figs, 4 page

    Anomalous magnetotransport in wide quantum wells

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    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 Shubnikov de Haas oscillations in the same manner as known from the quantum Hall effect. The onsets of plateaux in Rxy 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 Rxx and Rxy and fulfils exactly the Onsager-Casimir relation (Rij,kl(B) = Rkl,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.Comment: postscript file including 3 figs, 5 page

    Magnetotransport in wide parabolic PbTe quantum wells

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    The 3D- and 2D- behaviour of wide parabolic PbTe single quantum wells, which consist of PbTe p-n-p-structures, are studied theoretically and experimentally. A simple model combines the 2D- subband levels and the 3D-Landau levels in order to calculate the density of states in a magnetic field perpendicular to the 2D plane. It is shown that at a channel width of about 300nm on can expect to observe 3D- and 2D-behaviour at the same time. Magnetotransport experiments in selectively contacted Hall bar samples are performed at temperatures down to T = 50 mK and at magnetic fields up to B = 17 T.Comment: postscript file including 2 figs, 4 pages, Paper presented at EP2DS-XI, Nottingham 199

    Conductance Fluctuations in PbTe Wide Parabolic Quantum Wells

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    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 e^2/h. It is shown that the fluctuations have to be attributed to edge channel effects.Comment: postscript file including 3 figs, 3 pages, Paper presented at 3rd Int. Symposium on "New Phenomena in Mesoscopic Structures" in Maui, Hawaii 199

    Semileptonic B / Bs decays at Belle

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    The Belle experiment at the KEKB asymmetric energy e+e- collider recorded large data sets of both, B and Bs decays. Semileptonic decays B(s) -> X l nu (l = electron or muon) constitute approximately one fifth of the total decay width of B(s) mesons and play an important role in the determination of the CKM matrix elements V_ub and V_cb. Recent results from Belle are presented, including the study of B- -> Ds(*) K l nu, the first measurements of semi-inclusive modes B -> D(*) X l nu and the measurement of the inclusive branching fraction Bf(Bs -> X l nu).Comment: 6 pages, 5 figures, 36th International Conference on High Energy Physics. 4-11 July 2012. Melbourne, Australi

    The kinetic energy for the static SU(2) Polyakov line

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    At very high temperatures Yang--Mills theories can be described through perturbation theory. At the tree level the time components of the gluon fields decouple and yield a dimensionally reduced theory. The expectation value of the Polyakov loop then assumes values of the Z(N) center group. At intermediate temperatures, however, this is not true anymore. The time dependence shows up in loops. In a recent work we integrated out fast varying quantum fluctuations around background A_i and static A_4 fields. We assumed that these fields are slowly varying but that the amplitude of A_4 is arbitrary. As a result we obtained the kinetic energy terms for the Polyakov loop both for the electric and the magnetic sector of SU(2).Comment: 9 pages, 3 figures. Proceedings for Cracow School of Theoretical Physics, Zakopane, May 30 - June 08, 200
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