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978-3-8439-1229-7, Reihe Physik
Quantized conductance and evidence for zitterbewegung in InAs spin-filter cascades
60 Seiten, Dissertation Universität Hamburg (2013), Softcover, A5
InAs heterostructures provide long mean free paths that support ballistic transport in nanostructures. Their high Rashba spin-orbit interaction furthers spin-related phenomena like the intrinsic spin-Hall effect and spin precession. The intrinsic spin-Hall effect spatially separates spin-up and spin-down electrons provided the electron system is in the one-dimensional quantum limit where intersubband scattering is suppressed. The interplay of the spin-Hall effect and the spin precession leads to an oscillatory path of spin-polarized electrons that reminds one of Schrödinger's zitterbewegung for free electrons. All-semiconductor double Y-shaped InAs spin-filter cascades have been proposed that generate and detect polarized currents purely electrically as consequence of the intrinsic spin-Hall effect and the spin precession. The spin-filter cascades consist of two Y-shaped three-terminal junctions that are connected by a center wire. At the first stage two oppositely polarized currents are generated; one of them is deflected into the center wire. The spin-polarized current in the center wire is detected as conductance imbalance at the outputs of the second stage. The spin-polarized electrons in the center wire perform a zitterbewegung. Their position at the end of the center wire depends on the spin-precession length. In-plane magnetic fields add to the effective Rashba fields and thus change the spin-precession length and hence the conductances of the second filter's outputs. In this thesis top-gated InAs spin-filter cascades with quantum wires are fabricated and transport measurements in magnetic fields are presented. The top gate allows to control the electron density and to restrict the transport to the lowest one-dimensional subband in the whole cascade. Spin-resolved conductance quantization already at zero magnetic field indicates quasi-ballistic transport and strong Rashba spin-orbit interaction. A conductance imbalance at the second filter's outputs reveals the generation and detection of spin-polarized currents.
Oscillations of the conductance imbalance as a function of an in-plane magnetic field substantiate the interpretation of the conductance imbalance to be spin related and provides first evidence for the zitterbewegung in semiconductors.