arXiv subjects

Manuel Valin-Rodriguez

Publications and source records attributed to Manuel Valin-Rodriguez.

13 recordsLinked to original sources

arXiv2011

Predicted signatures of the intrinsic spin Hall effect in closed systems

We study a two-dimensional electron system in the presence of spin-orbit interaction. It is shown analytically that the spin-orbit interaction acts as a transversal effective electric field, whose orientation depends on the sign of the $\hat{z}$-axis spin projection. This effect doesn't require any driving external field and is inherent to the spin-orbit interactions present in semiconductor materials. Therefore, it should manifest in both closed and open systems. It is proposed an experiment to observe the intrinsic spin Hall effect in the far infrared absorption of an asymmetric semiconductor nanostructure.

cond-mat.mes-hall↗

arXiv2011

Spin current generation by helical states in a quasi-one-dimensional system

Time-reversal symmetry and rotational invariance in spin space characterize usual non-magnetic conductors. These symmetries give rise, at least, to four-fold degenerate multiplets which, by definition, exhibit a null total spin-momentum helicity. Thus, preventing a net spin transport. A proper choice of geometry along with the intrinsic symmetry of the Bychkov-Rashba spin-orbit interaction can be exploited to effectively reduce these two spin-related symmetries to the timereversal one. It is shown that, in an ideal geometry, a quantum dot with contacts having a specific geometry exhibit a single pair of helical propagating states which makes this system ideal for pure spin current generation. The strong quantization of the quantum dot's level structure would make this mechanism robust against temperature effects.

cond-mat.mes-hall↗

arXiv2005

Interplay between Zeeman interaction and spin-orbit coupling in a two-dimensional semiconductor system

We analyse the interplay between Dresselhaus, Bychkov-Rashba, and Zeeman interactions in a two-dimensional semiconductor quantum system under the action of a magnetic field. When a vertical magnetic field is considered, we predict that the interplay results in an effective cyclotron frequency that depends on a spin-dependent contribution. For in-plane magnetic fields, we found that the interplay induces an anisotropic effective gyromagnetic factor that depends on the orientation of the applied field as well as on the orientation of the electron momentum.

cond-mat.mes-hall↗

arXiv2005

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.

cond-mat.mes-hall↗

arXiv2004

Renormalization of spin-orbit coupling in quantum dots due to Zeeman interaction

We derive analitycally a partial diagonalization of the Hamiltonian representing a quantum dot including spin-orbit interaction and Zeeman energy on an equal footing. It is shown that the interplay between these two terms results in a renormalization of the spin-orbit intensity. The relation between this feature and experimental observations on conductance fluctuations is discussed, finding a good agreement between the model predictions and the experimental behavior.

cond-mat.mes-hall↗

arXiv2004

Zeeman energy and anomalous spin splitting in lateral GaAs quantum dots

The level splittings induced by a horizontal magnetic field in a parabolic two-dimensional quantum dot with spin-orbit interaction are obtained. Characteristic features induced by the spin-orbit coupling are the appearance of zero-field gaps as well as energy splittings that depend on the electronic state and the orientation of the magnetic field in the quantum-dot plane. It is suggested that these quantum-dot properties could be used to determine the Rashba and Dresselhaus spin-orbit intensities

cond-mat.mes-hall↗

arXiv2003

Spin splitting and precession in quantum dots with spin-orbit coupling: the role of spatial deformation

Extending a previous work on spin precession in GaAs/AlGaAs quantum dots with spin-orbit coupling, we study the role of deformation in the external confinement. Small elliptical deformations are enough to alter the precessional characteristics at low magnetic fields. We obtain approximate expressions for the modified $g$ factor including weak Rashba and Dresselhaus spin-orbit terms. For more intense couplings numerical calculations are performed. We also study the influence of the magnetic field orientation on the spin splitting and the related anisotropy of the $g$ factor. Using realistic spin-orbit strengths our model calculations can reproduce the experimental spin-splittings reported by Hanson et al. (cond-mat/0303139) for a one-electron dot. For dots containing more electrons, Coulomb interaction effects are estimated within the local-spin-density approximation, showing that many features of the non-iteracting system are qualitatively preserved.

cond-mat.mes-hall↗

arXiv2003

Electron spin precession in semiconductor quantum wires with Rashba spin-orbit coupling

The influence of the Rashba spin-orbit coupling on the electron spin dynamics is investigated for a ballistic semiconductor quantum wire with a finite width. We monitor the spin evolution using the time-dependent Schrödinger equation. The pure spin precession characteristic of the 1D limit is lost in a 2D wire with a finite lateral width. In general, the time evolution in the latter case is characterized by several frequencies and a nonrigid spin motion.

cond-mat.mes-hall↗

arXiv2002

Spin-Orbit induced semiconductor spin guides

The tunability of the Rashba spin-orbit coupling allows to build semiconductor heterostructures with space modulated coupling intensities. We show that a wire-shaped spin-orbit modulation in a quantum well can support propagating electronic states inside the wire only for a certain spin orientation and, therefore, it acts as an effective spin transmission guide for this particular spin orientation.

cond-mat.mes-hall↗

arXiv2002

Electronic spin precession in semiconductor quantum dots with spin-orbit coupling

The electronic spin precession in semiconductor dots is strongly affected by the spin-orbit coupling. We present a theory of the electronic spin resonance at low magnetic fields that predicts a strong dependence on the dot occupation, the magnetic field and the spin-orbit coupling strength. Coulomb interaction effects are also taken into account in a numerical approach.

cond-mat.mes-hall↗

arXiv2002

Spin switching in semiconductor quantum dots through spin-orbit coupling

The spin-orbit coupling influences the total spin of semiconductor quantum dots. We analyze the theoretical prediction for the combined effects of spin-orbit coupling, weak vertical magnetic fields and deformation of the dot. Our results allow the characterization of the quantum dots as spin switches, controllable with electric gates.

cond-mat.mes-hall↗

arXiv2002

Characterization of Bernstein modes in quantum dots

The dipole modes of non-parabolic quantum dots are studied by means of their current and density patterns as well as with their local absorption distribution. The anticrossing of the so-called Bernstein modes originates from the coupling with electron-hole excitations of the two Landau bands which are occupied at the corresponding magnetic fields. Non-quadratic terms in the potential cause an energy separation between bulk and edge current modes in the anticrossing region. On a local scale the fragmented peaks absorb energy in complementary spatial regions which evolve with the magnetic field.

cond-mat.mes-hall↗

arXiv2002

Role of spin-orbit coupling in the far infrared absorption of lateral semiconductor dots

We investigate the relevance of the spin-orit coupling to the far-infrared absorption of two-dimensional semiconductor dots. Varying the strength of the Dresselhaus term, a mechanism feasible in experiment by changing the dot width, distinctive splittings of the Kohn peak as well as additional low energy modes are predicted in a non-interacting model. Each mode has a spatial distribution of charge, perpendicular and in-plane spin densities that correlate in a peculiar way with the frequency and polarization of the external field. We study the robustness of these features against electron-electron interactions as well as the appearance of interaction-induced additional characteristics.

cond-mat.mes-hall↗