We predict that in a narrow gap III-V semiconductor quantum well or quantum wire, an observable electron spin current can be generated with a time dependent gate to modify the Rashba spin-orbit coupling constant. Methods to rectify the so generated AC current are discussed. An all-electric method of spin current detection is suggested, which measures the voltage on the gate in the vicinity of a 2D electron gas carrying a time dependent spin current. Both the generation and detection do not involve any optical or magnetic mediator.PACS numbers: 71.70. Ej, 72.25.Dc, One key issue in spintronics based on semiconductor is the efficient control of the spin degrees of freedom. Datta and Das 1 suggested the use of gate voltage to control the strength of Rashba spin-orbit interaction (SOI) 2 which is strong in narrow gap semiconductor heterostructures. In InAs-based quantum wells a variation of 50% of the SOI coupling constant was observed experimentally. 3,4Consequently, much interest has been attracted to the realization of spin polarized transistors and other devices based on using electric gate to control the spin dependent transport. 5Besides using a static gate to control the SOI strength and so control the stationary spin transport, new physical phenomena can be observed in time dependent spin transport under the influence of a fast varying gate voltage. Along this line, in this article we will consider a mechanism of AC spin current generation using time dependent gate. This mechanism employs a simple fact that the time variation of Rashba SOI creates a force which acts on opposite spin electrons in opposite directions. Inversely, when a gate is coupled to a nearby electron gas, the spin current in this electron gas also induces a variation of the gate voltage, and hence affects the electric current in the gate circuit. We will use a simple model to clarify the principle of such a new detection mechanism without any optical or magnetic mediator. The systems to be studied will be 1D electron gas in a semiconductor quantum wire (QWR) and 2D electron gas in a semiconductor quantum well (QW).We consider a model in which the Rashba SOI is described by the time dependent Hamiltonian H so (t) = α(t)( k ×ν) · s, where k is the wave vector of an electron, s is the spin operator, andν is the unit vector. For a QWRν is perpendicular to the wire axis, and for a QW perpendicular to the interfaces. The time dependence of the coupling parameter α(t) is caused by a time dependent gate. 6 To explain clearly the physical mechanisms leading to the spin current generation, we will first consider the 1D electron gas in a QWR, and assume α(t) to be a constant α for t<0, and α(t)=0 for t>0. For the 1D system we choose the x direction as the QWR axis and y axis parallel toν, to write the SOI coupling in the form H so (t)= α(t)k x s z . For t<0 the spin degeneracy of conduction electrons is lifted by SOI, producing a splitting ∆= αk x between s z =1/2 and s z =−1/2 bands, as shown in Fig. 1 by solid curves together with the Fermi energy...

The intrinsic spin-Hall effect on spin accumulation and electric conductance in a diffusive regime of a 2D electron gas has been studied for a 2D strip of a finite width. It is shown that the spin polarization near the flanks of the strip, as well as the electric current in the longitudinal direction exhibit damped oscillations as a function of the width and strength of the Dresselhaus spin-orbit interaction. Cubic terms of this interaction are crucial for spin accumulation near the edges. As expected, no effect on the spin accumulation and electric conductance have been found in case of Rashba spin-orbit interaction.PACS numbers: 72.25. Dc, 71.70.Ej, 73.40.Lq Spintronics is a fast developing area to use electron spin degrees of freedom in electronic devices [1]. One of its most challenging goals is to find a method for manipulating electron spins by electric fields. The spin-orbit interaction (SOI), which couples the electron momentum and spin, can be a mediator between the charge and spin degrees of freedom. Such a coupling gives rise to the so called spin-Hall effect (SHE) which attracted much interest recently. Due to SOI the spin flow can be induced perpendicular to the DC electric field, as has been predicted for systems containing spin-orbit impurity scatterers [2]. Later, similar phenomenon was predicted for noncentrosymmetric semiconductors with spin split electron and hole energy bands [3]. It was called the intrinsic spin-Hall effect, in contrast to the extrinsic impurity induced effect, because in the former case it originates from the electronic band structure of a semiconductor sample. Since the spin current carries the spin polarization, one would expect a buildup of the spin density near the sample boundaries. In fact, this accumulated polarization is a first signature of SHE which has been detected experimentally, confirming thus the extrinsic SHE [4] in semiconductor films and intrinsic SHE in a 2D hole gas [5]. On the other hand, there were still no experimental evidence of intrinsic SHE in 2D electron gases. The possibility of such an effect in macroscopic samples with a finite elastic mean free path of electrons caused recently much debates. It has been shown analytically [6,7,8,9,10,11] and numerically [12] that in such systems SHE vanishes at arbitrary weak disorder in DC limit, for isotropic, as well as anisotropic [10] impurity scattering, when SOI is represented by the so called Rashba interaction [13]. As one can expect in this case, there is no spin accumulation at the sample boundaries, except for the pockets near the electric contacts [7]. At the same time, the Dresselhaus SOI [14], which dominates in symmetric quantum wells, gives a finite spin-Hall conductivity [11]. The latter can be of the order of its universal value e/8π . The same has been shown for the cubic Rashba interaction in hole systems [12,15]. In this connection an important question is what sort of the spin accumulation could Dresselhaus SOI induce near sample boundaries. Another problem which, as far as we know,...

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Quantum transport in a narrow constriction, and in the presence of a finite-range time-modulated potential, is studied. The potential is taken the form V (x, t) = V0 θ(x)θ(a − x) cos(ωt), with a the range of the potential and x the transmission direction. As the chemical potential µ is increasing, the dc conductance G is found to exhibit dip, or peak, structures when µ is at nhω above the threshold energy of a subband. These structures in G are found in both the small a (a ≪ λF ) and the large a (a ≫ λF ) regime. The dips, which are associated with the formation of quasi-bound states, are narrower for smaller a, and for smaller V0. The locations of these dips are essentially fixed, with small shifts only in the case of large V0. Our results can be reduced to the limiting case of a delta-profile oscillating potential when both a and V0a are small. The assumed form of the time-modulated potential is expected to be realized in a gate-induced potential configuration.

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.