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,...

Recently, level crossings in the energy bands of crystals have been identified as a key signature for topological phase transitions. Using realistic models we show that the parameter space controlling the occurrence of level coincidences in energy bands has a much richer structure than anticipated previously. In particular, we identify robust level coincidences that cannot be removed by a small perturbation of the Hamiltonian compatible with the crystal symmetry. Different topological phases that are insulating in the bulk are then separated by a gapless (metallic) phase. We consider HgTe/CdTe quantum wells as a specific example.

Temporal universal conductance fluctuations (TUCF's) are observed in RuO 2 nanowires at cryogenic temperatures. The fluctuations persist up to very high T ∼ 10 K. Their root-mean-square magnitudes increase with decreasing T , reaching ∼ 0.2e 2 /h at T 2 K. These fluctuations are shown to originate from scattering of conduction electrons with rich amounts of mobile defects in artificially synthesized metal oxide nanowires. TUCF characteristics in both one-dimensional saturated and unsaturated regimes are identified and explained in terms of current theories. Furthermore, the TUCF's as a probe for the characteristic time scales of the mobile defects (two-level systems) are discussed.

Magnetic field dependent universal conductance fluctuations (UCF's) are observed in weakly disordered indium tin oxide nanowires from 0.26 K up to $\sim 25$ K. The fluctuation magnitudes increase with decreasing temperature, reaching a fraction of $e^2/h$ at $T \lesssim 1$ K. The shape of the UCF patterns is found to be very sensitive to thermal cycling of the sample to room temperatures, which induces irreversible impurity reconfigurations. On the other hand, the UCF magnitudes are insensitive to thermal cycling. Our measured temperature dependence of the root-mean-square UCF magnitudes are compared with the existing theory [C. W. J. Beenakker and H. van Houten, Phys. Rev. B \textbf{37}, 6544 (1988)]. A notable discrepancy is found, which seems to imply that the experimental UCF's are not cut off by the thermal diffusion length $L_T$, as would be expected by the theoretical prediction when $L_T < L_\varphi$, where $L_\varphi$ is the electron dephasing length. The approximate electron dephasing length is inferred from the UCF magnitudes and compared with that extracted from the weak-localization magnetoresistance studies. A reasonable semiquantitative agreement is observed.Comment: 11 pages, 9 figure

We propose and demonstrate theoretically that resonant inelastic scattering (RIS) can play an important role in dc spin current generation. The RIS makes it possible to generate dc spin current via a simple gate configuration: a single finger-gate that locates atop and orients transversely to a quantum channel in the presence of Rashba spin-orbit interaction. The ac biased finger-gate gives rise to a time-variation in the Rashba coupling parameter, which causes spin-resolved RIS, and subsequently contributes to the dc spin current. The spin current depends on both the static and the dynamic parts in the Rashba coupling parameter, α0 and α1, respectively, and is proportional to α0α 2 1 . The proposed gate configuration has the added advantage that no dc charge current is generated. Our study also shows that the spin current generation can be enhanced significantly in a double finger-gate configuration.PACS numbers: 72.25.Dc, 72.30.+q, Spintronics is important in both application and fundamental arenas [1,2]. A recent key issue of great interest is the generation of dc spin current (SC) without charge current. Various dc SC generation schemes have been proposed, involving static magnetic field [3,4], ferromagnetic material [5], or ac magnetic field [6]. More recently, Rashba-type spin-orbit interaction in 2DEG [7,8] has inspired attractive proposals for nonmagnetic dc SC generation [9,10,11]. Of these recent proposals, including a time-modulated quantum dot with a static spinorbit coupling [9], and time-modulations of a barrier and the spin-orbit coupling parameter in two spatially separated regions [10], the working principle is basically adiabatic quantum pumping. Hence simultaneous generation of both dc spin and charge current is the norm. The condition of zero dc charge current, however, is met only for some judicious choices for the values of the system parameters.It is known, on the other hand, that quantum transport in narrow channel exhibits RIS features when it is acted upon by a spatially localized time-modulated potential [12,13]. This RIS is coherent inelastic scattering, but with resonance at work, when the traversing electrons can make transitions to their subband threshold by emitting mhΩ [12,13]. Should this RIS become spin-resolved in a Rashba-type quantum channel (RQC), of which its Rashba coupling parameter is time-modulated locally, we will have a simpler route to the nonmagnetic generation of dc SC. Thus we opt to study, in this Letter, the RIS features in a RQC. As is required by a study on the RIS features, our study goes beyond the adiabatic regime.The system configuration considered is based on a RQC that forms out of a 2DEG in an asymmetric quantum well by the split-gate technique. As is depicted in Fig. 1(a), a finger gate (FG) is positioned above while it is separated from the RQC by an insulating layer. A local time-variation in the Rashba coupling parameter α(r, t) can be induced by ac biasing the FG [10,11]. The Hamiltonian is given by H = p 2 /2m + H so (r, t) + V c (y) where the R...