Semiclassical theory of anisotropic transport at LaAlO3/SrTiO3 interfaces under in-plane magnetic field

The unconventional magnetotransport at the interface between transition-metal oxides $LaAlO_3$ (LAO) and $SrTiO_3$ (STO) is frequently related to mobile electrons interacting with localized magnetic moments. However nature and properties of magnetism at this interface are not well understood so far. In this paper, we focus on transport effects driven by spin-orbit coupling and intentionally neglect possible strong correlations. The electrical resistivity tensor is calculated as a function of the magnitude and orientation of an external magnetic field parallel to the interface. The semiclassical Boltzmann equation is solved numerically for the two-dimensional system of spin-orbit coupled electrons accelerated by an electric field and scattered by spatially-correlated impurities. At temperatures of a few Kelvin and densities such that the chemical potential crosses the second pair of spin-orbit split bands, we find a strongly anisotropic modulation of the (negative) magnetoresistance above 10 T, characterized by multiple maxima and minima away from the crystalline axes. Along with the drop of the magnetoresistance, an abrupt enhancement of the transverse resistivity occurs. The angular modulation of the latter considerably deviates from a (low-field) sinusoidal dependence to a (high-field) step-like behaviour. These peculiar features are the consequences of the anisotropy of both (intra-band and inter-band ) scattering-amplitudes in the Brillouin zone when the relevant energy scales in the system - chemical potential, spin-orbit interaction and Zeeman energy - are all comparable to each other. The theory provides good qualitative agreement with experimental data in the literature.Comment: 14 pages, 9 figures, 2 appendices. Extended version with discussion section widely revised, additional results for different parameters in Appendix B, theoretical model presented in details in Appendix A. To be published in Phys. Rev.

Labour Migration Patterns in Europe: Recent Trends, Future Challenges

In the last few years, issues related to international migration are receiving increasing attention from policy makers. This reflects mainly the changes in the magnitude and composition of migration flows. Net migration into the EU has risen again during the period 1998 to 2003. With an overall level of around 4 per thousand, relative immigration levels into the EU appear to be at present somewhat higher than those into the US (3.3 per thousand). High irregular migration, with estimates of the relation between regular and irregular immigration running between 1:0,3 and 1:1, and high numbers of asylum applicants indicate an increase in migration pressure during the last decade. Major changes in the source and destination of migrants have also taken place: traditional receiving countries have lost prominence while Southern European countries, who were sending countries until fairly recently, have become receiving countries, and some Eastern European Member States are now both sending and receiving migrants.Labour migrations patterns, migrations flows, international migration, , Diez Guardia, Pichelmann

Topologically protected charge transfer along the edge of a chiral p\textit{p}-wave superconductor

The Majorana fermions propagating along the edge of a topological superconductor with $p_x+ip_y$ pairing deliver a shot noise power of $\frac{1}{2}\times e^2/h$ per eV of voltage bias. We calculate the full counting statistics of the transferred charge and find that it becomes trinomial in the low-temperature limit, distinct from the binomial statistics of charge-$e$ transfer in a single-mode nanowire or charge-$2e$ transfer through a normal-superconductor interface. All even-order correlators of current fluctuations have a universal quantized value, insensitive to disorder and decoherence. These electrical signatures are experimentally accessible, because they persist for temperatures and voltages large compared to the Thouless energy.Comment: 5 pages, 4 figures. v3 [post-publication]: added an appendix on the effect of a tunnel barrier at the normal-superconductor contac

Problema-experiencia para construir un modelo redox

En las aulas universitarias, existe una separación muy común entre “teoría”, “trabajo experimental” y “problemas”. En este trabajo se analizan los resultados de una experiencia que busca integrar esas tres actividades. En la Facultad de Ciencias Veterinarias de la UNCPBA, en Tandil (Argentina), a un grupo de alumnos de primer año, se les propuso un problema a investigar. Debían armar un diseño experimental, ejecutarlo, comparar resultados, extraer inferencias de un hecho empírico, y aplicar conceptos de óxido-reducción. Al comenzar la actividad se percibe el desconcierto de los estudiantes frente a esta problemática inusual para ellos (diseñar un trabajo experimental), pero luego la realizan en forma cooperativa y con entusiasmo

Onset of implant-related recombination in self-ion implanted and annealed crystalline silicon

The impact of residual recombination centers after low-energy self-implantation of crystalline silicon wafers and annealing at 900 °C has been determined by bulk carrier lifetime measurements as a function of implant dose. Doses below 10¹³cm⁻² resulted in no measurable increase in recombination, while higher doses caused a linear increase in the recombination center density. This threshold value corresponds to the known critical dose required for the formation of relatively stable dislocation loops during high temperature annealing.Deep level transient spectroscopy revealed a decrease in the vacancy-related defect concentration in the high-dose samples, which we interpret as reflecting an increase in the siliconinterstitial concentration. This suggests that siliconinterstitials, arising from the slowly dissolving dislocation loops, may be responsible for the increased recombination deep within the samples.This work has been supported by the Australian Research Council

Electron dynamics in intentionally disordered semiconductor superlattices

We study the dynamical behavior of disordered quantum-well-based semiconductor superlattices where the disorder is intentional and short-range correlated. We show that, whereas the transmission time of a particle grows exponentially with the number of wells in an usual disordered superlattice for any value of the incident particle energy, for specific values of the incident energy this time increases linearly when correlated disorder is included. As expected, those values of the energy coincide with a narrow subband of extended states predicted by the static calculations of Dom\'{\i}nguez-Adame {\em et al.} [Phys. Rev. B {\bf 51}, 14 ,359 (1994)]; such states are seen in our dynamical results to exhibit a ballistic regime, very close to the WKB approximation of a perfect superlattice. Fourier transform of the output signal for an incident Gaussian wave packet reveals a dramatic filtering of the original signal, which makes us confident that devices based on this property may be designed and used for nanotechnological applications. This is more so in view of the possibility of controllingthe outp ut band using a dc electric field, which we also discuss. In the conclusion we summarize our results and present an outlook for future developments arising from this work.Comment: 10 pagex, RevTex, 13 Postscript figures. Physical Review B (in press

Comparison of Navier-Stokes simulations with long-wave theory: Study of wetting and dewetting

The classical long-wave theory (also known as lubrication approximation) applied to fluid spreading or retracting on a solid substrate is derived under a set of assumptions, typically including small slopes and negligible inertial effects. In this work, we compare the results obtained by using the long-wave model and by simulating directly the full two-phase Navier-Stokes equations employing a volume-of-fluid method. In order to isolate the influence of the small slope assumption inherent in the long-wave theory, we present a quantitative comparison between the two methods in the regime where inertial effects and the influence of gas phase are negligible. The flow geometries that we consider include wetting and dewetting drops within a broad range of equilibrium contact angles in planar and axisymmetric geometries, as well as liquid rings. For perfectly wetting spreading drops we find good quantitative agreement between the models, with both of them following rather closely Tanner's law. For partially wetting drops, while in general we find good agreement between the two models for small equilibrium contact angles, we also uncover differences which are particularly evident in the initial stages of evolution, for retracting drops, and when additional azimuthal curvature is considered. The contracting rings are also found to evolve differently for the two models, with the main difference being that the evolution occurs on the faster time scale when the long-wave model is considered, although the ring shapes are very similar between the two models.Fil: Mahady, K.. New Jersey Institute of Technology. Department of Mathematical Sciences; Estados UnidosFil: Afkhami, S.. New Jersey Institute of Technology. Department of Mathematical Sciences; Estados UnidosFil: Diez, Javier Alberto. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Fisica Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tandil; ArgentinaFil: Kondic, L.. New Jersey Institute of Technology. Department of Mathematical Sciences; Estados Unido

Bloch oscillations in an aperiodic one-dimensional potential

We study the dynamics of an electron subjected to a static uniform electric field within a one-dimensional tight-binding model with a slowly varying aperiodic potential. The unbiased model is known to support phases of localized and extended one-electron states separated by two mobility edges. We show that the electric field promotes sustained Bloch oscillations of an initial Gaussian wave packet whose amplitude reflects the band width of extended states. The frequency of these oscillations exhibit unique features, such as a sensitivity to the initial wave packet position and a multimode structure for weak fields, originating from the characteristics of the underlying aperiodic potential.Comment: 6 pages, 7 figure

Differential hypertrophic effects of cardiotrophin-1 on adult cardiomyocytes from normotensive and spontaneously hypertensive rats

Cardiotrophin-1 (CT-1) produces longitudinal elongation of neonatal cardiomyocytes, but its effects in adult cardiomyocytes are not known. Recent observations indicate that CT-1 may be involved in pressure overload left ventricular hypertrophy (LVH). We investigated whether the hypertrophic effects of CT-1 are different in cardiomyocytes isolated from adult normotensive and spontaneously hypertensive rats (SHR). Hypertrophy was evaluated by planimetry and confocal microscopy, contractile proteins were quantified by Western blotting and real-time RT-PCR, and intracellular pathways were analyzed with specific chemical inhibitors. CT-1 increased c-fos and ANP expression (p<0.01) and cell area (p<0.01) in cardiomyocytes from both rat strains. In Wistar cells, CT-1 augmented cell length (p<0.01) but did not modify either the transverse diameter or cell depth. In SHR cells, CT-1 increased cell length (p<0.05), cell width (p<0.01) and cell depth, augmented the expression of myosin light chain-2v (MLC-2v) and skeletal alpha-actin (p<0.01) and enhanced MLC-2v phosphorylation (p<0.01). The blockade of gp130 or LIFR abolished CT-1-induced growth in the two cell types. All distinct effects observed in cardiomyocytes from SHR were mediated by STAT3. Baseline angiotensinogen expression was higher in SHR cells, and CT-1 induced a 1.7-fold and 3.2-fold increase of angiotensinogen mRNA in cardiomyocytes from Wistar rats and SHR respectively. In addition, AT1 blockade inhibited the specific effects of CT-1 in SHR cells. Finally, ex vivo determinations revealed that adult SHR exhibited enhanced myocardial CT-1 (mRNA and protein, p<0.01), increased cell width (p<0.01) and concentric LVH compared with pre-hypertensive SHR. These findings reveal a specific cell-broadening effect of CT-1 in cardiomyocytes from adult SHR and suggest that the hypertensive phenotype of these cells may influence the hypertrophic effects of CT-1, probably by means of an exaggerated induction of angiotensinogen expression. We suggest that CT-1 might facilitate LVH in genetic hypertension through a cross-talk with the renin-angiotensin system