The Ginzburg-Landau expansion and the slope of the upper critical field in disordered superconductors

It is shown that the slope of the upper critical field in superconductors with d pairing drops rapidly with increasing concentration of normal impurities, while in superconductors with anisotropic s pairing increases and reaches the well-known asymptotic level characteristic for the isotropic case. This difference makes it possible, in principle, to employ measurements of H _c 2 in disordered superconductors as an experimental method for determining the type of pairing in high-T _c superconductors and systems with heavy fermions. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 5, 347–352 (10 March 1996)     

Determination of heavy quark non-perturbative parametersfrom spectral moments in semileptonic B decays

Moments of the hadronic invariant mass and of the lepton energy spectra in semileptonic B decays have been determined with the data recorded by the DELPHI detector at LEP. From measurements of the inclusive b-hadron semileptonic decays, and imposing constraints from other measurements on b- and c-quark masses, the first three moments of the lepton energy distribution and of the hadronic mass distribution, have been used to determine parameters which enter into the extraction of |V_cb| from the measurement of the inclusive b-hadron semileptonic decay width. The values obtained in the kinetic scheme are: and include corrections at order 1/m_b³. Using these results, and present measurements of the inclusive semileptonic decay partial width of b-hadrons at LEP, an accurate determination of |V_cb| is obtained: Received: 26 April 2005, Revised: 16 September 2005, Published online: 16 November 2005     

Neutral meson oscillations and equivalence principle for particles and antiparticles

Oscillations of neutral meson (K ⁰-$ \overline {K^0 } $ \overline {K^0 } , D ⁰-$ \overline {D^0 } $ \overline {D^0 } , and B ⁰-$ \overline {B^0 } $ \overline {B^0 } are extremely sensitive to the meson and antimeson energies at rest. This energy is determined as mc ²—with the corresponding inertial mass—and as the energy of gravitational interaction. Assuming that the CPT theorem is correct for inertial masses and estimating the gravitational potential for which the largest contribution originates from the field of the galaxy center, we obtain the estimate from experimental data on K ⁰-$ \overline {K^0 } $ \overline {K^0 } oscillations:

Anomalies in the elastic properties of silicious iron single crystals at pressures of up to 9 GPa and the α−ɛ phase transformation

A Fe+5.07 at.%Si single crystal has been studied by ultrasonic-pulse technique. Its density and elastic constants were determined for p=0 and T=293 K. The dependence of the elastic properties of silicious iron on Si concentration was constructed. The compression, the effective elastic constants, and the Grüneisen parameters were measured at hydrostatic pressures of up to 9 GPa. It was found that for p=0, and . The elastic constants c ₄₄ and c′ increase linearly with pressure by 19.3 and 18.2% by p=9 GPa. The elastic anisotropy does not vary with pressure. For p>4 GPa, c ₁₁, c ₁₂, and K _S were observed to increase nonlinearly with decreasing pressure derivative. The Grüneisen parameter γ _LA decreases with pressure down to 0.70 at 9 GPa to become negative when extrapolated to the region of the α−ɛ phase transformation. The anomalies in c ₁₁ and the negative values of γ _LA for p>11 GPa indicate that the phase transformation in silicious iron at 13.5 GPa can take place by the crystallographic mechanism of the α−ɛ transformation in pure iron, i.e. by lattice compression in the [001] direction and shearing of the (110) planes along or . An assumption is put forward that pressure gives rise in silicious iron to sp-d hybridization, which results in increased screening of the ion-ion interaction and in anomalies in elastic properties. Similar phenomena are expected to occur in pure bcc Fe as well. Fiz. Tverd. Tela (St. Petersburg) 41, 516–522 (March 1999)     

Maximal Inequalities for CIR Processes

Let X be a Cox—Ingersoll—Ross (CIR) process given by

Measurement of the mass and width of the W boson

The mass and width of the W boson are measured using e⁺e^– → W⁺W^– events from the data sample collected by the OPAL experiment at LEP at centre-of-mass energies between 170 GeV and 209 GeV. The mass (m_W) and width (Γ_W) are determined using direct reconstruction of the kinematics of W⁺W^– → and W⁺W^– → events. When combined with previous OPAL measurements using W⁺W^– → events and the dependence on of the WW production cross-section at threshold, the results are determined to be

Quantum conformal superspace

For a compact connected orientablen-manifoldM, n 3, we study the structure ofclassical superspace ,quantum superspace ,classical conformal superspace , andquantum conformal superspace . The study of the structure of these spaces is motivated by questions involving reduction of the usual canonical Hamiltonian formulation of general relativity to a non-degenerate Hamiltonian formulation, and to questions involving the quantization of the gravitational field. We show that if the degree of symmetry ofM is zero, thenS,S ₀,C, andC ₀ areilh orbifolds. The case of most importance for general relativity is dimensionn=3. In this case, assuming that the extended Poincaré conjecture is true, we show that quantum superspaceS ₀ and quantum conformal superspaceC ₀ are in factilh-manifolds. If, moreover,M is a Haken manifold, then quantum superspace and quantum conformal superspace arecontractible ilh-manifolds. In this case, there are no Gribov ambiguities for the configuration spacesS ₀ andC ₀. Our results are applicable to questions involving the problem of thereduction of Einstein's vacuum equations and to problems involving quantization of the gravitational field. For the problem of reduction, one searches for a way to reduce the canonical Hamiltonian formulation together with its constraint equations to an unconstrained Hamiltonian system on a reduced phase space. For the problem of quantum gravity, the spaceC ₀ will play a natural role in any quantization procedure based on the use of conformal methods and the reduced Hamiltonian formulation.     

General theory of renormalization of gauge theories in nonlinear gauges

We discuss the general theory of renormalization of unbroken gauge theories in the nonlinear gauges in which the gauge-fixing term is of the form We show that higher loop renormalization modifiesfα [A] to contain ghost terms of the form and show how the corresponding ghost terms are deduced fromfα [A, c, c] uniquely. We show that the theory can be renormalized while preserving a modified form of BRS invariance by multiplicative and independent renormalizations onA, c, g, η, ζ, τ. We briefly discuss the independence of the renormalized S-matrix from η,ζ, τ.     

NMR dynamics in disordered magnets

The excitation dynamics of site diluted magnets can be described at low energies (long length scales) by magnons, and above a crossover frequency, ω_c, (short length scales) by fractons. The density of fracton states is given by , where is the fracton dimensionality. Dilution gives rise to a characteristic length ξ∝(p−p _c)^ν, wherep _c is the critical concentration for (magnetic) percolation. The crossover frequency ω_c is proportional to ξ^-1[1+(θ/2)], where θ is the rate at which the diffusion constant decays with distance for diffusion on an equivalent network. A fractal dimensionD describes the density of magnetic sites on the infinite network, and . For percolating networks, for all dimensions ≥2. Neutron scattering structure factor measurements by Uemura and Birgeneau compare well with calculations using fracton concepts. Magnons are extended at low energies, while the fracton states are geometrically localized, with a wave function envelope proportional to exp . Here, is the fracton length scale at frequency ω. The exponentd _ϕ lies between 1 andd _min, the chemical length index (of the order of 1.6 in three dimensions). The localization of the magnetic excitations causes a spread in the NMR relaxation rates. A given nuclear moment will experience only a limited set of fracton excitations, resulting in an overall non-exponential decay of the NMR relaxation signal. When strong cross-relaxation is present, the relaxation will be exponential, but the temperature dependence will be strongly altered from the concentrated result.     

Experimental test of special relativity by laser spectroscopy

The Doppler-free laser-spectroscopic frequency measurement of Doppler-shifted optical lines in forward and backward direction of a fast ion beam permits a sensitive test of the relativistic Doppler-formula and, hence, the relativistic time dilation factor . An experiment on metastable ⁷Li⁺, stored at a velocity of v = 0.064c in the Heidelberg heavy-ion storage ring TSR, has confirmed time dilation with unprecedented accuracy. Latest tests at two different ion-velocities (v = 0.03c and v = 0.064c) will enhance these measurements. An improved version of this experiment will be carried out at the experimental storage ring (ESR) at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt. The ESR permits ⁷Li⁺ to be stored at v = 0.33c which promises an improvement of the sensitivity to deviations from γ _SR by an order of magnitude. A first test at the ESR has shown the feasibility for this kind of experiment.     

Weakly Non-Ergodic Statistical Physics

For weakly non ergodic systems, the probability density function of a time average observable is where is the value of the observable when the system is in state j=1,…L. p _j ^eq is the probability that a member of an ensemble of systems occupies state j in equilibrium. For a particle undergoing a fractional diffusion process in a binding force field, with thermal detailed balance conditions, p _j ^eq is Boltzmann’s canonical probability. Within the unbiased sub-diffusive continuous time random walk model, the exponent 0<α<1 is the anomalous diffusion exponent 〈x ²〉∼t ^α found for free boundary conditions. When α→1 ergodic statistical mechanics is recovered . We briefly discuss possible physical applications in single particle experiments.     

NMR Studies on the Internal Structure of High-T c Superconductors and Other Anorganic Compounds

Spatially-resolved NMR is used to probe internal structures in highly correlated superconductors of optimally-doped (T _c = 85 K) and a heavy fermion superconductor CeCoIn₅ (T _c = 2.3 K). The characteristic change of the properties of ²⁰⁵Tl-NMR in the vortex state provides a clear evidence of the antiferromagnetic order in the vortex cores below 20 K in . We also obtain anomalous ¹¹⁵In-NMR spectra of CeCoIn₅, which provides a microscopic evidence for the occurrence of a spatially-modulated superconducting order parameter expected in a Fulde–Ferrel–Larkin–Ovchinnkov (FFLO) state.     

Search for double electron capture of 106Cd

A search for double electron capture of ¹⁰⁶Cd was performed at the Modane Underground Laboratory (4800 m w.e.) using a low-background and high-sensitivity multidetector spectrometer TGV-2 (Telescope Germanium Vertical). New limits on β ⁺/EC, EC/EC decays of ¹⁰⁶Cd were obtained from preliminary calculations of experimental data accumulated for 4800 h of measurement of 10 g of ¹⁰⁶Cd with enrichment of 75%. They are > 9.1 × 10¹⁸ yr, > 1.9 × 10¹⁹ yr for transitions to the first 2⁺, 511.9 keV excited state of ¹⁰⁶Pd, and > 1.3 × 10¹⁹ yr, > 6.2 × 10¹⁹ yr for transitions to the ground 0⁺ state of ¹⁰⁶Pd. All limits are given at 90% C.L. The text was submitted by the authors in English.     

Electric field strength at and near the cathode edge in a magnetically insulated coaxial diode

For an annular cathode in a coaxial diode it has been shown that the averaged electric field strength at the end face of the cathode, E_n, depends on the edge thickness h as

Two-photon axion decay in an external electromagnetic field

The amplitude of two-photon axion decay in a crossed field is calculated, taking into account the polarization states of the photons. The decay probability and amplitude in an external electromagnetic field exceed the decay probability and amplitude in vacuum even for values of the invariant parameter greater than the small quantity m _a/m _e. Astrophysical aspects associated with this circumstance are discussed. Zh. éksp. Teor. Fiz. 115, 385–391 (February 1999)     

Strongly elliptic operators with singular coefficients

In this paper, we deal with operators of the form

Comment on “Evaluation of concentration-depth profiles by sputtering in SIMS and AES” by S. Hofmann

The statistics of the sputtering process, which has been used to explain sputterbroadening effect due to surface roughness, has been treated with conditional probabilities. This results in the relationship, , instead of derived by S. Hofmann [Appl. Phys.9, 59 (1976)], where δz,z, and are the depth resolution, sputtered depth and sputtering yield, respectively.     

The electrochemical reactivity of the NiP<Subscript>3</Subscript> skutterudite-type phase with lithium

We report the electrochemical Li reactivity of the cubic NiP₃ phase, a candidate for anode applications for Li-ion batteries. NiP₃ reacts with nine lithium per formula unit leading to a first cycle reversible capacity of 1,475 mAh/g at an average potential of 0.9 V vs. Li+/Li°. Electrochemical measurements and complementary X-ray diffraction showed that NiP₃ presents a conversion process competing with an insertion process. A good cycleability may only be obtained on a limited potential window, excluding the low-potential region. This paper was presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Al,F-doped new perovskite lithium fast ion conductor Li3x La2/3−x□1/3−2x Ti1−y Al y O3−y F y (x=0.11)

Al, F-doped new perovskite lithium ion conductors (x=0.11) have been prepared by solid state reaction. It is found that a pure perovskite-structured phase with space group of P4mm(99) exits in the composition range of 0<y≤0.10. The sample with y=0.02 possesses the highest ionic conductivity of 1.06×10⁻³ S/cm at room temperature, and its decomposing voltage is 2.3 V. The factors affecting the conductivity of this system are discussed.     

Transport properties of CsHSO4 investigated by impedance spectroscopy and nuclear magnetic resonance

Transport properties of the superprotonic conductor, CsHSO₄, have been investigated by impedance spectroscopy and nuclear magnetic resonance (NMR). It has been found that both, conductivity (σ) and NMR diffusion (D _NMR) are practically isotropic in the high-conductive (superprotonic) phase (above 414 K). The NMR diffusion coefficient, D _NMR , increases rapidly and discontinuously at the melting point (~490 K). The temperature change of D _NMR in the superprotonic phase is characterized by a smaller activation energy compared to that in the liquid state. The values calculated from the Nernst-Einstein relation practically coincide with D _NMR in the superprotonic phase, i.e., the Haven ratio is close to unity. This indicates that in this phase the proton motion is rather uncorrelated.