Superconducting Properties of MgCNi3 Films

We report the magnetotransport properties of thin polycrystalline films of the recently discovered non-oxide perovskite superconductor MgCNi3. CNi3 precursor films were deposited onto sapphire substrates and subsequently exposed to Mg vapor at 700 C. We report transition temperatures (Tc) and critical field values (Hc2) of MgCNi3 films ranging in thickness from 7.5 nm to 100 nm. Films thicker than ~40 nm have a Tc ~ 8 K, and an upper critical field Hc2 ~ 14 T, which are both comparable to that of polycrystalline powders. Hall measurements in the normal state give a carrier density, n =-4.2 x 10^22 cm^-3, that is approximately 4 times that reported for bulk samples.Comment: submitted to PR

Electronic transport in EuB6_6

EuB$_6$ is a magnetic semiconductor in which defects introduce charge carriers into the conduction band with the Fermi energy varying with temperature and magnetic field. We present experimental and theoretical work on the electronic magnetotransport in single-crystalline EuB$_6$. Magnetization, magnetoresistance and Hall effect data were recorded at temperatures between 2 and 300 K and in magnetic fields up to 5.5 T. The negative magnetoresistance is well reproduced by a model in which the spin disorder scattering is reduced by the applied magnetic field. The Hall effect can be separated into an ordinary and an anomalous part. At 20 K the latter accounts for half of the observed Hall voltage, and its importance decreases rapidly with increasing temperature. As for Gd and its compounds, where the rare-earth ion adopts the same Hund's rule ground state as Eu$^{2+}$ in EuB$_{6}$, the standard antisymmetric scattering mechanisms underestimate the $size$ of this contribution by several orders of magnitude, while reproducing its $shape$ almost perfectly. Well below the bulk ferromagnetic ordering at $T_C$ = 12.5 K, a two-band model successfully describes the magnetotransport. Our description is consistent with published de Haas van Alphen, optical reflectivity, angular-resolved photoemission, and soft X-ray emission as well as absorption data, but requires a new interpretation for the gap feature deduced from the latter two experiments.Comment: 35 pages, 12 figures, submitted to PR

Markov Properties of Electrical Discharge Current Fluctuations in Plasma

Using the Markovian method, we study the stochastic nature of electrical discharge current fluctuations in the Helium plasma. Sinusoidal trends are extracted from the data set by the Fourier-Detrended Fluctuation analysis and consequently cleaned data is retrieved. We determine the Markov time scale of the detrended data set by using likelihood analysis. We also estimate the Kramers-Moyal's coefficients of the discharge current fluctuations and derive the corresponding Fokker-Planck equation. In addition, the obtained Langevin equation enables us to reconstruct discharge time series with similar statistical properties compared with the observed in the experiment. We also provide an exact decomposition of temporal correlation function by using Kramers-Moyal's coefficients. We show that for the stationary time series, the two point temporal correlation function has an exponential decaying behavior with a characteristic correlation time scale. Our results confirm that, there is no definite relation between correlation and Markov time scales. However both of them behave as monotonic increasing function of discharge current intensity. Finally to complete our analysis, the multifractal behavior of reconstructed time series using its Keramers-Moyal's coefficients and original data set are investigated. Extended self similarity analysis demonstrates that fluctuations in our experimental setup deviates from Kolmogorov (K41) theory for fully developed turbulence regime.Comment: 25 pages, 9 figures and 4 tables. V3: Added comments, references, figures and major correction

Energy loss due to defect formation from 206Pb recoils in SuperCDMS germanium detectors

The Super Cryogenic Dark Matter Search experiment at the Soudan Underground Laboratory studied energy loss associated with defect formation in germanium crystals at mK temperatures using in situ 210Pb sources. We examine the spectrum of 206Pb nuclear recoils near its expected 103 keV endpoint energy and determine an energy loss of (6:08 ± 0:18)%, which we attribute to defect formation. From this result and using TRIM simulations, we extract the first experimentally determined average displacement threshold energy of 19.7+0.6−0.5 eV for germanium. This has implications for the analysis thresholds of future germanium-based dark matter searches

A new perspective on the normalization of invariant measures for loss networks and other product form systems

Loss networks have proved to be a vital tool in the study of telecommunication networks, computer performance, and resource allocation problems. For a large subset of these models, the invariant measure is of a product form. The existence of efficient procedures to normalize a product-form invariant measure is essential for analysis of the underlying system. Choudhury et al. [1-4] have recently presented a number of algorithms based upon Fourier analysis for the normalization of product-form invariant measures for specific systems. Bean and Stewart [5] discussed related work for the normalization of product-form invariant measures for closed queueing networks. In this paper, we present a simple unifying framework within which to study these algorithms. This framework is significant as it suggests a number of extensions to these algorithms and simplifies their derivation. (C) 2000 Elsevier Science Ltd