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

Quantum correlations in nanostructured two-impurity Kondo systems

We study the ground-state entanglement properties of nanostructured Kondo systems consisting of a pair of impurity spins coupled to a background of confined electrons. The competition between the RKKY-like coupling and the Kondo effect determines the development of quantum correlations between the different parts of the system. A key element is the electronic filling due to confinement. An even electronic filling leads to results similar to those found previously for extended systems, where the properties of the reduced impurity-spin subsystem are uniquely determined by the spin correlation function defining a one-dimensional phase space. An odd filling, instead, breaks spin-rotation symmetry unfolding a two-dimensional phase space showing rich entanglement characteristics as, e.g., the requirement of a larger amount of entanglement for the development of non-local correlations between impurity spins. We check these results by numerical simulations of elliptic quantum corrals with magnetic impurities at the foci as a case study.Comment: Submitted for publication. 8 pages, 4 figures. Revised versio

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

Quantum network approach to spin interferometry driven by Abelian and non-Abelian fields

We present a theory of conducting quantum networks that accounts for Abelian and non-Abelian fields acting on spin carriers. We apply this approach to model the conductance of mesoscopic spin interferometers of different geometry (such as squares and rings), reproducing recent experimental findings in nanostructured InAsGa quantum wells subject to Rashba spin-orbit and Zeeman fields (as, e.g., the manipulation of Aharonov-Casher interference patterns by geometric means). Moreover, by introducing an additional field-texture engineering, we manage to single out a previously unnoticed spin-phase suppression mechanism. We notice that our approach can also be used for the study of complex networks and the spectral properties of closed systems

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

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