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Register a new userElectron-electron interactions in a one-dimensional quantum wire spin filter
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The combined presence of a Rashba and a Zeeman effect in a ballistic one-dimensional conductor generates a spin pseudogap and the possibility to propagate a beam with well defined spin orientation. Without interactions transmission through a barrier gives a relatively well polarized beam. Using renormalization group arguments, we examine how electron-electron interactions may affect the transmission coefficient and the polarization of the outgoing beam.
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We consider the adiabatic pumping of charge through a mesoscopic one dimensional wire in the presence of electron-electron interactions. A two-delta potential model is used to describe the wire, which allows to obtain exactly the scattering matrix coefficients, which are renormalized by the interactions. Two periodic drives, shifted one from another, are applied at two locations of the wire in order to drive a current through it in the absence of bias. Analytical expressions are obtained for the pumped charge, current noise, and Fano factor in different regimes. This allows to explore pumping for the whole parameter range of pumping strengths. We show that, working close to a resonance is necessary to have a comfortable window of pumping amplitudes where charge quantization is close to the optimum value: a single electron charge is transferred in one cycle. Interactions can improve the situation, the charge $Q$ is closer to one electron charge and noise is reduced, following a $Q (1-Q)$ behavior, reminiscent of the reduction of noise in quantum wires by $T (1-T)$, where $T$ is the energy transmission coefficient. For large pumping amplitudes, this charge vanishes, noise also decreases but slower than the charge.
Understanding the flow of spins in magnetic layered structures has enabled an increase in data storage density in hard drives over the past decade of more than two orders of magnitude1. Following this remarkable success, the field of spintronics or spin-based electronics is moving beyond effects based on local spin polarisation and is turning its attention to spin-orbit interaction (SOI) effects, which hold promise for the production, detection and manipulation of spin currents, allowing coherent transmission of information within a device. While SOI-induced spin transport effects have been observed in two- and three-dimensional samples, these have been subtle and elusive, often detected only indirectly in electrical transport or else with more sophisticated techniques. Here we present the first observation of a predicted spin-orbit gap in a one-dimensional sample, where counter-propagating spins, constituting a spin current, are accompanied by a clear signal in the easily-measured linear conductance of the system.
We study the spin states of a few-electron quantum dot defined in a two-dimensional electron gas, by applying a large in-plane magnetic field. We observe the Zeeman splitting of the two-electron spin triplet states. Also, the one-electron Zeeman splitting is clearly resolved at both the zero-to-one and the one-to-two electron transition. Since the spin of the electrons transmitted through the dot is opposite at these two transitions, this device can be employed as an electrically tunable, bipolar spin filter. Calculations and measurements show that higher-order tunnel processes and spin-orbit interaction have a negligible effect on the polarization.
In the integer quantum Hall (IQH) regime, an antidot provides a finite, controllable `edge of quantum Hall fluid that is an ideal laboratory for investigating the collective dynamics of large numbers of interacting electrons. Transport measurements of single antidots probe the excitation spectra of the antidot edge, and gate-defined antidot devices offer the flexibility to vary both the antidots dimensions and its couplings to extended IQH edge modes which serve as leads. We also use the spin-selectivity of the IQH edge modes to perform spin-resolved transport measurements, from which we can infer the antidot spin-structure. This thesis describes a combination of such transport experiments and related computational models designed to investigate the effects of electron-electron interactions in quantum antidots, with general implications for the physics of spin and charge in IQH systems.
We study the shot noise (nonequilibrium current fluctuation) associated with dynamic nuclear polarization in a nonequilibrium quantum wire (QW) fabricated in a two-dimensional electron gas. We observe that the spin-polarized conductance quantization of the QW in the integer quantum Hall regime collapses when the QW is voltage biased to be driven to nonequilibrium. By measuring the shot noise, we prove that the spin polarization of electrons in the QW is reduced to $sim 0.7$ instead of unity as a result of electron-nuclear spin-flip scattering. The result is supported by Knight shift measurements of the QW using resistively detected NMR.
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