Spin interference in silicon three-terminal one-dimensional rings

We present the first findings of the spin transistor effect in the Rashba gate-controlled ring embedded in the p-type self-assembled silicon quantum well that is prepared on the n-type Si (100) surface. The coherence and phase sensitivity of the spin-dependent transport of holes are studied by varying the value of the external magnetic field and the bias voltage that are applied perpendicularly to the plane of the double-slit ring. Firstly, the amplitude and phase sensitivity of the 0.7(2e^2/h) feature of the hole quantum conductance staircase revealed by the quantum point contact inserted in the one of the arms of the double-slit ring are found to result from the interplay of the spontaneous spin polarization and the Rashba spin-orbit interaction. Secondly, the quantum scatterers connected to two one-dimensional leads and the quantum point contact inserted are shown to define the amplitude and the phase of the Aharonov-Bohm and the Aharonov-Casher conductance oscillations.Comment: 8 pages, 5 figure

Spin-dependent transport in p+-CdBxF2-x - n-CdF2 planar structures

The CV measurements and tunneling spectroscopy are used to study the ballistic transport of the spin-polarized holes by varying the value of the Rashba spin-orbit interaction (SOI) in the p-type quantum well prepared on the surface of the n-CdF2 bulk crystal. The findings of the hole conductance oscillations in the plane of the p-type quantum well that are due to the variations of the Rashba SOI are shown to be evidence of the spin transistor effect, with the amplitude of the oscillations close to e2/h.Comment: 5 pages, 6 figure

Spin-dependent electron-impurity scattering in two-dimensional electron systems

We present a theoretical study of elastic spin-dependent electron scattering caused by a charged impurity in the vicinity of a two-dimensional electron gas. We find that the symmetry properties of the spin-dependent differential scattering cross section are different for an impurity located in the plane of the electron gas and for one at a finite distance from the plane. We show that in the latter case asymmetric (`skew') scattering can arise if the polarization of the incident electron has a finite projection on the plane spanned by the normal vector of the two-dimensional electron gas and the initial propagation direction. In specially preparated samples this scattering mechanism may give rise to a Hall-like effect in the presence of an in-plane magnetic field.Comment: 4.1 pages, 2 figure

Skew scattering due to intrinsic spin-orbit coupling in a two-dimensional electron gas

We present the generalization of the two-dimensional quantum scattering formalism to systems with Rashba spin-orbit coupling. Using symmetry considerations, we show that the differential scattering cross section depends on the spin state of the incident electron, and skew scattering may arise even for central spin-independent scattering potentials. The skew scattering effect is demonstrated by exact results of a simple hard wall impurity model. The magnitude of the effect for short-range impurities is estimated using the first Born approximation. The exact formalism we present can serve as a foundation for further theoretical investigations.Comment: 4 pages, 3 figur

INTEGRAL observations of the black hole candidate H 1743-322 in outburst

INTEGRAL made 3 observations in 2003 April of the black hole candidate H 1743-322 during the rising part, and close to the maximum, of an outburst. H 1743-322 was previously observed in outburst in 1977-1978. The source is located in a crowded region of the sky (l = 357 deg, b = -2 deg) and at least 18 sources are clearly detected in the field of view of the gamma-ray imager during a 277 ksec exposure. These are well known persistent X-ray binaries and 3 transient sources in outburst. The combined 5-200 keV JEM-X and SPI spectrum of H 1743-322 is well fit with an absorbed ((2.5 10E22 atom/cm2) soft (photon index 2.70 +/- 0.09) power-law model consistent with J 1743-322 being in a high/soft state.Comment: 5 pages. Figs. 2 and 3 are best viewed in color. To appear in INTEGRAL special edition of A&A

V-V Bond-Length Fluctuations in Vox

We report a significantly stronger suppression of the phonon contribution to the thermal conductivity in VOx than can be accounted for by disorder of the 16 % atomic vacancies present in VO. Since the transition from localized to itinerant electronic behavior is first-order and has been shown to be characterized by bond-length fluctuations in several transition-metal oxides with the perovskite structure, we propose that cooperative V-V bond-length fluctuations play a role in VO similar to the M-O bond-length fluctuations in the perovskites. This model is able to account for the strong suppression of the thermal conductivity, the existence of a pseudogap confirmed by thermoelectric power, an anomalously large Debye-Waller factor, the temperature dependence of the magnetic susceptibility, and the inability to order atomic vacancies in VO.Comment: 5 pages, 5 figure

Dynamic correlations in stochastic rotation dynamics

The dynamic structure factor, vorticity and entropy density dynamic correlation functions are measured for Stochastic Rotation Dynamics (SRD), a particle based algorithm for fluctuating fluids. This allows us to obtain unbiased values for the longitudinal transport coefficients such as thermal diffusivity and bulk viscosity. The results are in good agreement with earlier numerical and theoretical results, and it is shown for the first time that the bulk viscosity is indeed zero for this algorithm. In addition, corrections to the self-diffusion coefficient and shear viscosity arising from the breakdown of the molecular chaos approximation at small mean free paths are analyzed. In addition to deriving the form of the leading correlation corrections to these transport coefficients, the probabilities that two and three particles remain collision partners for consecutive time steps are derived analytically in the limit of small mean free path. The results of this paper verify that we have an excellent understanding of the SRD algorithm at the kinetic level and that analytic expressions for the transport coefficients derived elsewhere do indeed provide a very accurate description of the SRD fluid.Comment: 33 pages including 16 figure

Manifestly Gauge-Invariant General Relativistic Perturbation Theory: II. FRW Background and First Order

In our companion paper we identified a complete set of manifestly gauge-invariant observables for general relativity. This was possible by coupling the system of gravity and matter to pressureless dust which plays the role of a dynamically coupled observer. The evolution of those observables is governed by a physical Hamiltonian and we derived the corresponding equations of motion. Linear perturbation theory of those equations of motion around a general exact solution in terms of manifestly gauge invariant perturbations was then developed. In this paper we specialise our previous results to an FRW background which is also a solution of our modified equations of motion. We then compare the resulting equations with those derived in standard cosmological perturbation theory (SCPT). We exhibit the precise relation between our manifestly gauge-invariant perturbations and the linearly gauge-invariant variables in SCPT. We find that our equations of motion can be cast into SCPT form plus corrections. These corrections are the trace that the dust leaves on the system in terms of a conserved energy momentum current density. It turns out that these corrections decay, in fact, in the late universe they are negligible whatever the value of the conserved current. We conclude that the addition of dust which serves as a test observer medium, while implying modifications of Einstein's equations without dust, leads to acceptable agreement with known results, while having the advantage that one now talks about manifestly gauge-invariant, that is measurable, quantities, which can be used even in perturbation theory at higher orders.Comment: 51 pages, no figure

The AGN nature of 11 out of 12 Swift/RXTE unidentified sources through optical and X-ray spectroscopy

The Swift Burst Alert Telescope (BAT) is performing a high Galactic latitude survey in the 14-195 keV band at a flux limit of ~10^{-11} erg cm^{-2} s^{-1}, leading to the discovery of new high energy sources, most of which have not so far been properly classified. A similar work has also been performed with the RXTE slew survey leading to the discovery of 68 sources detected above 8 keV, many of which are still unclassified. Follow-up observations with the Swift X-ray Telescope (XRT) provide, for many of these objects, source localization with a positional accuracy of few arcsec, thus allowing the search for optical counterparts to be more efficient and reliable. We present the results of optical/X-ray follow-up studies of 11 Swift BAT detections and one AGN detected in the RXTE Slew Survey, aimed at identifying their counterparts and at assessing their nature. These data allowed, for the first time, the optical classification of 8 objects and a distance determination for 3 of them. For another object, a more refined optical classification than that available in the literature is also provided. For the remaining sources, optical spectroscopy provides a characterization of the source near in time to the X-ray measurement. The sample consists of 6 Seyfert 2 galaxies, 5 Seyferts of intermediate type 1.2-1.8, and one object of Galactic nature - an Intermediate Polar (i.e., magnetic) Cataclysmic Variable. Out of the 11 AGNs, 8 (~70%) including 2 Seyferts of type 1.2 and 1.5, are absorbed with NH > 10^{22} cm^{-2}. Up to 3 objects could be Compton thick (i.e. NH > 1.5 x 10^{24} cm^{-2}), but only in one case (Swift J0609.1-8636) does all the observational evidence strongly suggests this possibility.Comment: 50 pages, including 16 figures and 7 tables. Accepted for publication in Ap