Intrinsic spin dynamics in semiconductor quantum dots

We investigate the characteristic spin dynamics corresponding to semiconductor quantum dots within the multiband envelope function approximation (EFA). By numerically solving an $8\times8$ $k\cdot p$ Hamiltonian we treat systems based on different III-V semiconductor materials.It is shown that, even in the absence of an applied magnetic field, these systems show intrinsic spin dynamics governed by intraband and interband transitions leading to characteristic spin frequencies ranging from the THz to optical frequencies.Comment: to be published in Nanotechnology. Separated figure file

Persistent spin and charge currents and magnification effects in open ring conductors subject to Rashba coupling

We analyze the effect of Rashba spin-orbit coupling and of a local tunnel barrier on the persistent spin and charge currents in a one-dimensional conducting Aharonov-Bohm (AB) ring symmetrically coupled to two leads. First, as an important consequence of the spin-splitting, it is found that a persistent spin current can be induced which is not simply proportional to the charge current. Second, a magnification effect of the persistent spin current is shown when one tunes the Fermi energy near the Fano-type antiresonances of the total transmission coefficient governed by the tunnel barrier strength. As an unambiguous signature of spin-orbit coupling we also show the possibility to produce a persistent pure spin current at the interference zeros of the transmittance. This widens the possibilities of employing mesoscopic conducting rings in phase-coherent spintronics applications.Comment: 6 pages, 5 figures, to appear in PR

Charge transport in two dimensional electron gas/superconductor junctions with Rashba spin-orbit coupling

We have studied the tunneling conductance in two dimensional electron gas / insulator / superconductor junctions in the presence of Rashba spin-orbit coupling (RSOC). It is found that for low insulating barrier the tunneling conductance is suppressed by the RSOC while for high insulating barrier it is almost independent of the RSOC. We also find the reentrant behavior of the conductance at zero voltage as a function of RSOC for intermediate insulating barrier strength. The results are essentially different from those predicted in ferromagnet / superconductor junctions. The present derivation of the conductance is applicable to arbitrary velocity operator with off-diagonal components.Comment: 8 pages, 6 figure

Spin Transport in Disordered Two-Dimensional Hopping Systems with Rashba Spin-Orbit Interaction

The influence of Rashba spin-orbit interaction on the spin dynamics of a topologically disordered hopping system is studied in this paper. This is a significant generalization of a previous investigation, where an ordered (polaronic) hopping system has been considered instead. It is found, that in the limit, where the Rashba length is large compared to the typical hopping length, the spin dynamics of a disordered system can still be described by the expressions derived for an ordered system, under the provision that one takes into account the frequency dependence of the diffusion constant and the mobility (which are determined by charge transport and are independent of spin). With these results we are able to make explicit the influence of disorder on spin related quantities as, e.g., the spin life-time in hopping systems.Comment: 12 pages, 6 figures, some clarifications adde

Nuclear Dynamics During Landau-Zener Singlet-Triplet Transitions in Double Quantum Dots

We consider nuclear spin dynamics in a two-electron double dot system near the intersection of the electron spin singlet $S$ and the lower energy component $T_{+}$ of the spin triplet. The electron spin interacts with nuclear spins and is influenced by the spin-orbit coupling. Our approach is based on a quantum description of the electron spin in combination with the coherent semiclassical dynamics of nuclear spins. We consider single and double Landau-Zener passages across the $S$-$T_{+}$ anticrossings. For linear sweeps, the electron dynamics is expressed in terms of parabolic cylinder functions. The dynamical nuclear polarization is described by two complex conjugate functions $\Lambda ^{\pm}$ related to the integrals of the products of the singlet and triplet amplitudes ${\tilde{c}}_{S}^{\ast}{\tilde{c}}_{T_{+}}$ along the sweep. The real part $P$ of $\Lambda ^{\pm}$ is related to the $S$-$T_{+}$ spin-transition probability, accumulates in the vicinity of the anticrossing, and for long linear passages coincides with the Landau-Zener probability $P_{LZ}=1-e^{-2\pi \gamma}$, where $\gamma$ is the Landau-Zener parameter. The imaginary part $Q$ of $\Lambda^{+}$ is specific for the nuclear spin dynamics, accumulates during the whole sweep, and for $\gamma \gtrsim 1$ is typically an order of magnitude larger than $P$. $Q$ has a profound effect on the nuclear spin dynamics, by (i) causing intensive shake-up processes among the nuclear spins and (ii) producing a high nuclear spin generation rate when the hyperfine and spin-orbit interactions are comparable in magnitude. We find analytical expressions for the back-action of the nuclear reservoir represented via the change in the Overhauser fields the electron subsystem experiences.Comment: 19 pages, 5 figure

Electron locking in semiconductor superlattices

We describe a novel state of electrons and phonons arising in semiconductor superlattices (SSL) due to strong electron-phonon interactions. These states are characterized by a localization of phonons and a self-trapping or locking of electrons in one or several quantum wells due to an additional, deformational potential arising around these locking wells in SSL. The effect is enhanced in a longitudinal magnetic field. Using the tight-binding and adiabatic approximations the whole energy spectrum of the self-trapped states is found and accurate, analytic expressions are included for strong electron-phonon coupling. Finally, we discuss possible experiments which may detect these predicted self-trapped states.Comment: 8 pages, 2 figures. Please note that the published article has the title 'Electron locking in layered structures by a longitudinal magnetic field

Spontaneous generation of spin-orbit coupling in magnetic dipolar Fermi gases

The stability of an unpolarized two-component dipolar Fermi gas is studied within mean-field theory. Besides the known instability towards spontaneous magnetization with Fermi sphere deformation, another instability towards spontaneous formation of a spin-orbit coupled phase with a Rashba-like spin texture is found. A phase diagram is presented and consequences are briefly discussed

Improved limit on electron neutrino charge radius through a new evaluation of the weak mixing angle

We have obtained a new limit on the electron neutrino effective charge radius from a new evaluation of the weak mixing angle by a combined fit of all electron-(anti)neutrino electron elastic scattering measurements. Weak mixing angle is found to be sin^2 theta_W=0.259 \pm 0.025 in the low energy regime below 100 MeV. The electron neutrino charge radius squared is bounded to be in the range -0.13 10^-32 cm^2 < r^2 < 3.32 10^-32 cm^2 at 90 % C.L. Both results improve previously published analyses. We also discuss perspectives of future experiments to improve these constraints.Comment: 10 pages, 2 figures. Final published versio

Spontaneous spin-polarized current in a nonuniform Rashba interaction system

We investigate the electron transport through a two-dimensional semiconductor with a nonuniform Rashba spin-orbit interaction. Due to the combination of the coherence effect and the Rashba interaction, a spontaneous spin-polarized current emerges in the absence of any magnetic material and magnetic field. For a two-terminal device, only the local current contains polarization; however, with a four-terminal setup, a polarized total current is produced. This phenomenon may offer a novel way for generating a spin-polarized current, replacing the traditional spin-injection method.Comment: 4 pages, 4 figure

Two Anderson impurities in a 2D host with Rashba spin-orbit interaction

We have studied the two-dimensional two-impurity Anderson model with additional Rashba spin-orbit interaction by means of the modified perturbation theory. The impurity Green's functions we have constructed exactly reproduce the first four spectral moments. We discuss the height and the width of the even/odd Kondo peaks as functions of the inter-impurity distance and the Rashba energy $E_R$ (the strength of the Rashba spin-orbit interaction). For small impurity separations the Kondo temperature shows a non-monotonic dependence on $E_R$ being different in the even and the odd channel. We predict that the Kondo temperature has only almost linear dependence on $E_R$ and not an exponential increase with $E_R$Comment: To be published in Phys. Rev.