Mesoscopic effects in adiabatic spin pumping

Spin-Hall conductivity and Hall angle in a two-dimensional system with impurities in the presence of spin–orbit interactions

We investigate the spin-torque-dependent Spin Hall phenomenon in a two-dimensional tight-binding system in the presence of Rashba and Dresselhaus spin–orbit interactions and random static impurities. We employ the Matsubara Green function techniques to calculate the relaxation time caused by the scattering of electrons by impurities. The longitudinal and transverse conductivities are next calculated with the help of the Kubo formalism. We have also calculated the spin Hall angle for the present model and studied its dependence on spin–orbit interactions and impurity strength. Finally, we explore the effect of interplay between the Rashba and Dresselhaus interactions on the spin-Hall effect.

Quantum Adiabatic Pumping in Rashba- Dresselhaus-Aharonov-Bohm Interferometer

We investigate the quantum adiabatic pumping effect in an interferometer attached to two one-dimensional leads. The interferometer is subjected to an Aharonov-Bohm flux and Rashba-Dresselhaus spin-orbit interaction. Using Brouwer’s formula and rigorous scattering eigenstates, we obtained the general closed formula for the pumping Berry curvatures depending on spin for general interferometers when the external control parameters only modulate the scattering eigenstates and corresponding eigenvalues. In this situation, pumping effect is absent in the combination of the control parameters of Aharonov-Bohm flux and spin-orbit interaction strength. We have shown that finite pumping is possible by modulating both Rashba and Dresselhaus interaction strengths and explicitly demonstrated the spin-pumping effect in a diamond-shaped interferometer made of four sites.

Generation of large spin and valley currents in a quantum pump based on molybdenum disulfide

Generation of large currents, versatile functionality, and simple structures are of fundamental importance in the development of adiabatic quantum pump devices with nanoscale dimensions. In the present study, we propose an adiabatic quantum pump with a simple structure based on molybdenum disulfide, MoS₂, to generate large spin and valley resolved currents. We show that pure and fully polarized spin and valley currents can be easily generated by employing two potential gates and using an exchange magnetic field. Unlike graphene and silicene, in order to induce a valley resolved current in MoS₂, one does not need to induce strain and apply an electric field. The spin and valley resolved currents are completely coupled together, so that the spin up (down) current is exactly equal to the valley K(K') current. Hence, we can detect the valley resolved current by utilizing more straightforward and simple methods used for the detection of spin resolved currents. The other prominent feature of this proposed pump is its large current, which is two and three orders of magnitude larger than the maximum current of similar pump structures based on silicene and graphene, respectively. The results of this study are promising for the fabrication of quantum pumps with large spin and valley resolved currents, which opens up the possibility of further development of spintronics and valleytronics in 2D nanostructures.

Efficient spin filter using multi-terminal quantum dot with spin-orbit interaction

We propose a multi-terminal spin filter using a quantum dot with spin-orbit interaction. First, we formulate the spin Hall effect (SHE) in a quantum dot connected to three leads. We show that the SHE is significantly enhanced by the resonant tunneling if the level spacing in the quantum dot is smaller than the level broadening. We stress that the SHE is tunable by changing the tunnel coupling to the third lead. Next, we perform a numerical simulation for a multi-terminal spin filter using a quantum dot fabricated on semiconductor heterostructures. The spin filter shows an efficiency of more than 50% when the conditions for the enhanced SHE are satisfied.PACS numbers: 72.25.Dc,71.70.Ej,73.63.Kv,85.75.-d.

Purely electric spin pumping in one dimension

We show theoretically that a simple one-dimensional system (such as metallic wire) can display quantum spin pumping possibly without pushing any charge. It is achieved by applying two slowly varying orthogonal gate electric fields on different sections of the wire, thereby generating local spin-orbit (Rashba) terms such that unitary transformations at different places do not commute. This construction is a unique manifestation of a spin-orbit observable effect in purely one-dimensional systems with potentials respecting time-reversal symmetry.

Generation and detection of spin current in the three-terminal quantum dot

We propose a novel device composed of a quantum dot tunneling coupled to ferromagnetic, superconducting, and normal-metal leads. This device can generate, manipulate, and detect pure spin current through the interplay between the spin-polarized quantum transport and the Andreev reflection. The spin current in this device is a well-defined conserved current since there is no need for any spin-orbit coupling. The proposed device is realizable using present nanotechnology.

Spin density induced by equilibrium spin current in a magnetic field

We propose theoretically to use an external magnetic field to detect the equilibrium spin current which flows in a narrow strip. The spin current is generated by two noncollinear ferromagnets attached to the strip and the applied magnetic field is perpendicular to the plane of the strip. It is demonstrated by using the Keldysh Green's function that the interaction between the spin current and the magnetic field causes an antisymmetrical spin density at the two lateral edges of the strip. The spin density can be directly measured experimentally. Its magnitude and direction can be readily controlled by the magnetizations of the ferromagnets. The proposed scheme offers a new approach to the detection of the pure spin current.

Strain-induced coupling of spin current to nanomechanical oscillations

We propose a setup which allows us to couple the electron spin degree of freedom to the mechanical motions of a nanomechanical system not involving any of the ferromagnetic components. The proposed method employs the strain-induced spin-orbit interaction of electrons in narrow gap semiconductors. We have shown how this method can be used for detection and manipulation of the spin flow through a suspended rod in a nanomechanical device.

Pure spin current from one-photon absorption of linearly polarized light in noncentrosymmetric semiconductors

We show that one-photon absorption of linearly polarized light should produce pure spin currents in noncentrosymmetric semiconductors, including even bulk GaAs. We present 14x14 k.p model calculations of the effect in GaAs, including strain, and pseudopotential calculations of the effect in wurtzite CdSe.

Adiabatic pumping in the mixed-valence and Kondo regimes

We investigate adiabatic pumping through a quantum dot with a single level in the mixed-valence and Kondo regimes using the slave boson mean field approximation. The pumped current is driven by a gauge potential due to time-dependent tunneling barriers as well as by the modulation of the Friedel phase. The sign of the former contribution depends on the strength of the Coulomb interaction. Under finite magnetic fields, the separation of the spin and charge currents peculiar to the Kondo effect occurs.