We present analytical and numerical results for the effect of Rashba spin-orbit coupling on band structure, transport, and interaction effects in quantum wires when the spin precession length is comparable to the wire width. The situation with only the lowest spin-split subbands occupied is particularly interesting because electrons close to Fermi points of the same chirality can have approximately parallel spins. We discuss consequences for spin-dependent transport and effective Tomonaga-Luttinger descriptions of interactions in the quantum wire.PACS numbers: 71.10. Pm, Spin-dependent transport phenomena are currently attracting a lot of interest because of their potential for future electronic device applications [1]. Basic design proposals for spin-controlled field-effect switches [2,3] use the fact that electron waves with opposite spin aquire different phase factors during their propagation in the presence of Rashba spin-orbit coupling[4] (RSOC). The latter arises due to structural inversion asymmetry in quantum heterostructures [5,6] where two-dimensional (2D) electron systems are realized. The single-electron Hamiltonian is then of the form [7] H 2D = H 0 + H so wherewith m denoting the effective electron mass [26]. Possibility to tune the strength of RSOC, measured here in terms of the characteristic wave vector k so , by external gate voltages has been demonstrated experimentally [8,9,10]. As a manifestation of broken spin-rotational invariance, eigenstates of H 2D which are labeled by a 2D wave vector k have their spin pointing in the direction perpendicular to k. Hence, no common spin quantization axis can be defined for eigenstates when spin-orbit coupling is present. Confining the 2D electrons further to form a quantum wire, one might naively expect to again be able to define a global spin quantization axis, as the propagation direction of electrons in a one-dimensional (1D) system is fixed. However, this turns out to be correct only for a truly 1D electron system with vanishing width. In real quantum wires, such a situation is approximately realized when the spin-precession length[2] π/k so is much larger than wire width. Another way to formulate this condition is to say that the characteristic energy scale ∆ so =h 2 k 2 so /2m for RSOC is small compared to the energy spacing of 1D subbands. For a quantum wire defined by a parabolic confining potential, e.g.,the latter would behω. When spin-orbit coupling is not small (i.e., when ∆ so ∼hω for the case of parabolic confinement), hybridization of 1D subbands for opposite spins becomes important, resulting in the deformation of electronic dispersion relations [11]. The effect of this deformation on transport properties has been the subject of recent investigation [11], e.g., with respect to implications for the modulation of spin-polarized conductances as a function of RSOC strength [12] which is the principle of operation for spin-controlled field-effect devices [2,3].Here we present results for the detailed spin structure of electron states in a qua...

The presence of spin-orbit coupling affects the spontaneously flowing persistent currents in mesoscopic conducting rings. Here we analyze their dependence on magnetic flux with emphasis on identifying possibilities to prove the presence and extract the strength of Rashba spin splitting in low-dimensional systems. Effects of disorder and mixing between quasi-onedimensional ring subbands are considered. The spin-orbit coupling strength can be inferred from the values of flux where sign changes occur in the persistent charge current. As an important consequence of the presence of spin splitting, we identify a nontrivial persistent spin current that is not simply proportional to the charge current. The different flux dependences of persistent charge and spin currents are a unique signature of spin-orbit coupling affecting the electronic structure of the ring.

We present a diagrammatic real-time approach to adiabatic pumping of electrons through interacting quantum dots. Performing a systematic perturbation expansion in the tunnel-coupling strength, we compute the charge pumped through a single-level quantum dot per pumping cycle. The combination of Coulomb interaction and quantum fluctuations, accounted for in contributions of higher order in the tunnel coupling, modifies the pumping characteristics via an interactiondependent renormalization of the quantum-dot level. The latter is even responsible for the dominant contribution to the pumped charge when pumping via time-dependent tunnel-coupling strengths.

We study subgap transport from a superconductor through a double quantum dot with large on-site Coulomb repulsion to two normal leads. Non-local superconducting correlations in the double dot are induced by the proximity to the superconducting lead, detectable in non-local Andreev transport that splits Cooper pairs in locally separated, spin-entangled electrons. We find that the $I$--$V$ characteristics are strongly asymmetric: for a large bias voltage of certain polarity, transport is blocked by populating the double dot with states whose spin symmetry is incompatible with the superconductor. Furthermore, by tuning gate voltages one has access to splitting of the Andreev excitation energies, which is visible in the differential conductance.Comment: 5 pages, 4 figure