Conditions for Adiabatic Spin Transport in Disordered Systems

We address the controversy concerning the necessary conditions for the observation of Berry phases in disordered mesoscopic conductors. For this purpose we calculate the spin-dependent conductance of disordered two-dimensional structures in the presence of inhomogeneous magnetic fields. Our numerical results show that for both, the overall conductance and quantum corrections, the relevant parameter defining adiabatic spin transport scales with the square root of the number of scattering events, in generalization of Stern's original proposal [Phys. Rev. Lett. 68, 1022 (1992)]. This could hinder a clear-cut experimental observation of Berry phase effects in diffusive metallic rings.Comment: 5 pages, 4 figures. To appear in Phys. Rev. B (Rapid Communications

Spin Filter Effects in Mesoscopic Ring Structures

We study the spin-dependent conductance of ballistic mesoscopic ring systems in the presence of an inhomogeneous magnetic field. We show that, for the setup proposed, even a small Zeeman splitting can lead to a considerable spin polarisation of the current. Making use of a spin-switch effect predicted for such systems we propose a device of two rings connected in series that in principle allows for both creating and coherently controlling spin polarized currents at low temperatures.Comment: 5 pages, 8 figure

Orbital entanglement and electron localization in quantum wires

We study the signatures of disorder in the production of orbital electron entanglement in quantum wires. Disordered entanglers suffer the effects of localization of the electron wave function and random fluctuations in entanglement production. This manifests in the statistics of the concurrence, a measure of the produced two-qubit entanglement. We calculate the concurrence distribution as a function of the disorder strength within a random-matrix approach. We also identify significant constraints on the entanglement production as a consequence of the breaking/preservation of time-reversal symmetry. Additionally, our theoretical results are independently supported by simulations of disordered quantum wires based on a tight-binding model

Spin interference effects in ring conductors subject to Rashba coupling

Quantum interference effects in rings provide suitable means for controlling spin at mesoscopic scales. Here we apply such control mechanisms to coherent spin-dependent transport in one- and two-dimensional rings subject to Rashba spin-orbit coupling. We first study the spin-induced modulation of unpolarized currents as a function of the Rashba coupling strength. The results suggest the possibility of all-electrical spintronic devices. Moreover, we find signatures of Berry phases in the conductance previously unnoticed. Second, we show that the polarization direction of initially polarized, transmitted spins can be tuned via an additional small magnetic control flux. In particular, this enables to precisely reverse the polarization direction at half a flux quantum. We present full numerical calculations for realistic two-dimensional ballistic microstructures and explain our findings in a simple analytical model for one-dimensional rings.Comment: 8 pages, 5 figures. Submitted to Phys. Rev. B, final versio

Aharonov-Bohm Physics with Spin II: Spin-Flip Effects in Two-dimensional Ballistic Systems

We study spin effects in the magneto-conductance of ballistic mesoscopic systems subject to inhomogeneous magnetic fields. We present a numerical approach to the spin-dependent Landauer conductance which generalizes recursive Green function techniques to the case with spin. Based on this method we address spin-flip effects in quantum transport of spin-polarized and -unpolarized electrons through quantum wires and various two-dimensional Aharonov-Bohm geometries. In particular, we investigate the range of validity of a spin switch mechanism recently found which allows for controlling spins indirectly via Aharonov-Bohm fluxes. Our numerical results are compared to a transfer-matrix model for one-dimensional ring structures presented in the first paper (Hentschel et al., submitted to Phys. Rev. B) of this series.Comment: 29 pages, 15 figures. Second part of a series of two article

Magnetic switching of spin-scattering centers in Dresselhaus [110] circuits

Spin carriers subject to Dresselhaus [110] (D110) spin-orbit coupling (SOC) gather null spin phases in closed circuits, contrary to usual Rashba and Dresselhaus [001] SOC. We show that D110 spin phases can be activated in square circuits by introducing an in-plane Zeeman field, where localized field inhomogeneities act as effective spin-scattering centers. Our simulations show rich interference patterns in the quantum conductance, which work as maps for a geometric classification of the propagating spin states. We also find that disorder facilitates low-field implementations.Comment: evised version, 6 pages + supplemental materia

Quantum Transport in Nonuniform Magnetic Fields: Aharonov-Bohm Ring as a Spin Switch

We study the spin-dependent magneto conductance in mesoscopic rings subject to an inhomogeneous in-plane magnetic field. We show that the polarization direction of transmitted spin-polarized electrons can be controlled via an additional magnetic flux such that spin flips are induced at half a flux quantum. This quantum interference effect is independent of the strength of the nonuniform field applied. We give an analytical explanation for one-dimensional rings and numerical results for corresponding ballistic microstructures.Comment: 5 pages, 3 figures. To be published in Physical Review Letter