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Nanowire double quantum dots occupied by an even number of electrons are investigated in the context of energy level structure revealed by electric dipole spin resonance measurements. We use a numerically exact configuration interaction approach up to six electrons for systems tuned to a Pauli spin blockade regime. We point out the differences between the spectra of systems with two and a greater number of electrons. For two electrons the unequal length of the dots results in a different effective g factor in the dots as observed by the recent experiments. For an increased number of electrons the g-factor difference between the dots appears already for symmetric systems and it is greatly amplified when the dots are of unequal length. We find that the energy splitting defining the resonant electric dipole spin frequency can be quite precisely described by the two electrons involved in the Pauli blockade with the lower-energy occupied states forming a frozen core. [ABSTRACT FROM AUTHOR]

Electron flow through a quantum point contact in the presence of spin-orbit coupling is investigated theoretically in the context of the scanning gate microscopy (SGM) conductance mapping. Although in the absence of the floating gate the spin-orbit coupling does not significantly alter the conductance, we find that the angular dependence of the SGM images of the electron flow at the conductance plateaus is substantially altered as the spin-orbit interaction mixes the orbital modes that enter the quantum point contact. The radial interference fringes that are obtained in the SGM maps at conductance steps are essentially preserved by the spin-orbit interaction as backscattering by the tip preserves the electron spin although the effects of the mode mixing are visible. [ABSTRACT FROM AUTHOR]

A complete numerical description of the charge and spin dynamics of a two-electron system confined in narrow nanowire quantum dots under oscillating electric field is presented in the context of recent electric dipole spin resonance experiments. We find that the spin-orbit coupling results in lifting the spin blockade by phonon mediated relaxation provided that the initially occupied state is close in energy to the ground state. This leads to suppression of the blockade from the triplet state with spins polarized parallel to the external magnetic field B. At higher B, after singlet-triplet ground-state transition a new channel for lifting the Pauli blockade opens which results in an appearance of additional resonance lines. The calculated signatures of this transition are consistent with recent experimental results. [ABSTRACT FROM AUTHOR]

One- and two-electron systems confined in single and coupled quantum dots defined within a nanowire with a finite radius are studied in the context of spin-orbit coupling effects. The anisotropy of the spin-orbit interaction is discussed in terms of the system geometry and orientation of the external magnetic field vector. We find that there are easy and hard spin-polarization axes, and in the quantum dot with strong lateral confinement electron spin becomes well defined in spite of the presence of spin-orbit coupling. We present an analytical solution for the one-dimensional limit and study its validity for nanowires of finite radii by comparing the results with a full three-dimensional calculation. The results are also compared with the recent measurements of the effective Landé factor and avoided crossing width anisotropy in InSb nanowire quantum dots [ S. Nadj-Perge et al. Phys. Rev. Lett. 108 166801 (2012)]. [ABSTRACT FROM AUTHOR]

Spin rotations induced by an ac electric field in a two-electron double quantum dot are studied by an exact numerical solution of the time-dependent Schrödinger equation in the context of recent electric-dipole spin resonance experiments on gated nanowires. We demonstrate that the splitting of the main resonance line by the spin exchange coupling is accompanied by the appearance of fractional resonances and that both these effects are triggered by interdot tunnel coupling. We find that the ac-driven system generates residual but distinct harmonics of the driving frequency, which are amplified when tuned to the main transition frequency. The mechanism is universal for electron systems in electrically driven potentials and works also in the absence of electron-electron interaction or spin-orbit coupling. [ABSTRACT FROM AUTHOR]

Electron transport through a spin-orbit-coupled quantum ring is investigated within linear response theory. We show that the finite width of the ring results in the appearance of Fano resonances in the conductance. This turns out to be a consequence of the spin-orbit interaction that leads to a breaking of the parity of the states localized in the ring. The resonances appear when the system is close to maxima of Aharonov-Casher conductance oscillations where spin transfer is heavily modified. When the spin-orbit coupling strength is detuned from the Aharonov-Casher maxima the resonances are broadened resulting in a dependence of the spin transport on the electron Fermi energy in contrast to predictions from one-dimensional models. [ABSTRACT FROM AUTHOR]

We study avoided crossings opened by spin-orbit interaction in the energy spectra of one- and two-electron anisotropic quantum dots in perpendicular magnetic field. We find that for simultaneously present Rashba and Dresselhaus interactions the width of avoided crossings and the effective g factor depend on the dot orientation within the (001) crystal plane. The extreme values of these quantities are obtained for [110] and [110] orientations of the dot. The width of singlet-triplet avoided crossing changes between these two orientations by as much as two orders of magnitude. The discussed modulation results from the orientation-dependent strength of the Zeeman interaction, which tends to polarize the spins in the direction of the external magnetic field and thus remove the spin-orbit coupling effects. [ABSTRACT FROM AUTHOR]

Orbital effects of a magnetic field in a proximitized semiconductor nanowire are studied in the context of the spatial extent of Majorana bound states. We develop an analytical model that explains the impact of concurring effects of paramagnetic coupling of the nanowire bands via the kinetic energy operator and spin-orbit interaction on the Majorana modes. We find that the perpendicular field, so far considered to be detrimental to the Majorana fermion formation, is, in fact, helpful in establishing the topological zero-energy modes in a finite system due to significant decrease in the Majorana decay length. [ABSTRACT FROM AUTHOR]

We consider optical signatures of valence band mixing in positive trion and exciton complexes in vertically stacked InGaAs quantum dots. We use the configuration interaction method and an axially symmetric four-band Luttinger-Kohn Hamiltonian (KL) that allows for heavy-hole and light-hole band mixing due to spin-orbit interaction. A scalar effective hole mass model is also included for comparison. We found essential differences (i.e., different recombination patterns) between the KL and separated-bands model spectra. In the weak-coupling regime for KL model, we obtained a good agreement with experimentally observed X patterns in contrast to the scalar effective mass model. [ABSTRACT FROM AUTHOR]

We consider scanning gate microscopy imaging of the double slit interference for a pair of quantum point contacts (QPCs) defined within the two-dimensional electron gas. The interference is clearly present in the scattered electron wave functions for each of the incident subbands. Nevertheless, we find that the interference is generally missing in the experimentally accessible conductance maps for many incident subbands. We explain this finding on the basis of the Landauer approach. A setup geometry allowing for observation of the double slit interference by scanning gate microscopy is proposed. [ABSTRACT FROM AUTHOR]

We consider spin rotations in single- and two-electron quantum dots that are driven by an external ac electric field with two mechanisms that couple the electron spatial motion and the spin degree of freedom: the spin-orbit interaction and a random fluctuation of the Overhauser field due to nuclear spin bath. We perform a systematic numerical simulation of the driven system using a finite-difference approach with an exact account taken for the electron-electron correlation. The simulation demonstrates that the electron oscillation in fluctuating nuclear field is translated into an effective magnetic field during the electron wave packet motion. The effective magnetic field drives the spin transitions according to the electric-dipole spin resonance mechanism. We find distinct signatures of selection rules for direct and higher order transitions in terms of the spin-orbital symmetries of the wave functions. The selection rules are violated by the random fluctuation of the Overhauser field. [ABSTRACT FROM AUTHOR]