Quasiparticle trapping in Meissner and vortex states of mesoscopic superconductors

Nowadays superconductors serve in numerous applications, from high-field magnets to ultra-sensitive detectors of radiation. Mesoscopic superconducting devices, i.e. those with nanoscale dimensions, are in a special position as they are easily driven out of equilibrium under typical operating conditions. The out-of-equilibrium superconductors are characterized by non-equilibrium quasiparticles. These extra excitations can compromise the performance of mesoscopic devices by introducing, e.g., leakage currents or decreased coherence times in quantum devices. By applying an external magnetic field, one can conveniently suppress or redistribute the population of excess quasiparticles. In this article we present an experimental demonstration and a theoretical analysis of such effective control of quasiparticles, resulting in electron cooling both in the Meissner and vortex states of a mesoscopic superconductor. We introduce a theoretical model of quasiparticle dynamics which is in quantitative agreement with the experimental data

Assessment of the U and Co magnetic moments in UCoGe by X-ray magnetic circular dichroism

The ferromagnetic superconductor UCoGe has been investigated by high field X-ray magnetic circular dichroism (XMCD) at the U-M$_{4,5}$ and Co/Ge-K edges. The analysis of the branching ratio and XMCD at the U-M$_{4,5}$ edges reveals that the U-5$f$ electrons count is close to 3. The orbital ($\sim0.70\,\mu_B$) and spin ($\sim-0.30\,\mu_B$) moments of U at 2.1K and 17T (H//c) have been determined. Their ratio ($\sim-2.3$) suggests a significant delocalization of the 5$f$ electron states. The similar field dependences of the local U/Co and the macroscopic magnetization indicate that the Co moment is induced by the U moment. The XMCD at the Co/Ge-K edges reveal the presence of small Co-4$p$ and Ge-4$p$ orbital moments parallel to the macroscopic magnetization. In addition, the Co-3$d$ moment is estimated to be at most of the order of 0.1$\mu_B$ at 17T. Our results rule out the possibility of an unusual polarisability of the U and Co moments as well as their antiparallel coupling. We conclude that the magnetism which mediates the superconductivity in UCoGe is driven by U.Comment: 4 figures + supplementary materia

Double crystal x-ray diffraction simulations of diffusion in semiconductor microstructures

Diffusion in group IV, III-V and II-VI semiconductors is an interesting problem not only from a fundamental physics viewpoint but also in practical terms, since it could determine the useful lifetime of a device. Any attempt to control the amount of diffusion in a semiconductor device, whether it be a quantum well structure or not, requires an accurate determination of the diffusion coefficient. The present theoretical study shows that this could be achieved via x-ray diffraction studies in quantum well structures. It is demonstrated that the rocking curves of single quantum wells are not sensitive to diffusion. However the intensity of the first order satellite, which is characteristic of superlattice rocking curves, is strongly dependent upon diffusion and it is proposed that this technique could be used to measure the diffusion coefficient D. © 1998 American Institute of Physics

Asymptotic confidence interval for R2 in multiple linear regression

Following White's approach of robust multiple linear regression, we give asymptotic confidence intervals for the multiple correlation coefficient R2 under minimal moment conditions. We also give the asymptotic joint distribution of the empirical estimators of the individual R2's. Through different sets of simulations, we show that the procedure is indeed robust (contrary to the procedure involving the near exact distribution of the empirical estimator of R2 is the multivariate Gaussian case) and can be also applied to count linear regression

Thermal conductivity through the quantum critical point in YbRh2Si2 at very low temperature

The thermal conductivity of YbRh2Si2 has been measured down to very low temperatures under field in the basal plane. An additional channel for heat transport appears below 30 mK, both in the antiferromagnetic and paramagnetic states, respectively below and above the critical field suppressing the magnetic order. This excludes antiferromagnetic magnons as the origin of this additional contribution to thermal conductivity. Moreover, this low temperature contribution prevails a definite conclusion on the validity or violation of the Wiedemann-Franz law at the field-induced quantum critical point. At high temperature in the paramagnetic state, the thermal conductivity is sensitive to ferromagnetic fluctuations, previously observed by NMR or neutron scattering and required for the occurrence of the sharp electronic spin resonance fracture.Comment: 11 pages + Supplementary Material

Mineralization process of spring in carbonate coastal aquifer in the massif Bokkoya (Central Rif, Morocco)

The study focuses on the monitoring of physico-chemical parameters and major chemistry elements in water from six springs and sinks during two seasons, rainy and dry. Samples taken in the coastal karst aquifer massif Bokkoya Al-Hoceima, were analyzed for their chemical quality and to quantify their state of anthropogenic and / or natural contamination, scientific and practical interest, because local population used to supply drinking water. The waters of the internal Rif region are highly mineralized and marked by a chloride-sodium or sodium-sulfated facies to connect mainly to a process of marine intrusion and dissolution of evaporitic minerals included in the on-site rocks. This mineralization of marine origin is partly due to the intensive exploitation of groundwater but also to landslides, that are known in the area, and which accelerate the phenomenon of saltwater intrusion in the coastal karstic aquifer. The salinity of this water presente levels of salinization C3 and C4 as classified by Wilcox log and water of the Bokkoya massif were qualified as very hard. The comparison of hydrochemical results to the quality standards for drinking water set by the World Health Organization shows that the majority of the water withdrawal is not suitable for consumption, especially because of the high levels of EC, TDS and Cl- related to marine intrusion, together with the urban pollution factor which increases the content of NO-3 in waters

Superconducting Gap of UCoGe probed by Thermal Transport

Thermal conductivity measurements in the superconducting state of the ferromagnet UCoGe were performed at very low temperatures and under magnetic field on samples of different qualities and with the heat current along the three crystallographic axis. This allows to disentangle intrinsic and extrinsic effects, confirm the situation of multigap superconductivity and shed new light on the situation expected or claimed for the gap in these ferromagnetic superconductors, like evidences of absence of "partially gapped" Fermi surfaces.Comment: 6 pages, 5 figures. To be appeared in Physical Review Rapid Communicatio

Hydrochemical characterization of groundwater in the Nekor basin located in the North-East of the Rif of Morocco

 In order to evaluate the physicochemical quality of the groundwater of the Nekor watershed (central Rif area in Morocco) and to explain the origin of the mineralization of these waters, we have analyzed the major elements and traces in water samples taken from 17 wells distributed along the basin. This study showed that the samples of water are very charged with a very important mineralization (≥ 1500 mg / l). The Piper diagram allowed us to define dominant Ca-SO4 or Mg-SO4 hydrochemical facies in upstream of the basin. In downstream of the basin Na-SO4 or Na-Cl is the dominant facies. The analyzes of the trace elements show very high levels of manganese, aluminum and iron with contents exceeding those set by the WHO recommendations.The geochemical study shows that the water-rock interaction is predominant in the aquifer. The water saturation indices indicate that these waters are supersaturated in carbonate minerals.The Principal Component Analysis (PCA) and the analysis of the reports of the major elements allowed us the classification of the waters and the determination of the correlation between the various parameters. Two major phenomena in the acquisition of mineralization of water have been put in evidence. The main phenomenon is the dissolution of the rock by the contact water rock due to the important residence time in the aquifer. The second phenomenon is associated to the supply of nutrients and therefore with the exchange and recharge of the aquifer. The use of hierarchical cluster analysis (HCA) technique revealed three homogeneous groups.