Collective modes in charged superconductors near Tc

The dynamics of charged superconductors is described within a phenomenological model. It exhibits near T_c a screened propagating mode, which represents high frequency second sound. The damping is due to friction, to the conversion of normal to superfluid, and diffusion.     

Specific heat of type II superconductors near Tc

An explanation is suggested for the anomaly that has been observed in the mixed to normal state specific heat discontinuity of type II superconductors in low fields, near T_c.     

Correlation of Tc with structure in the density of states in the new high-Tc superconductors

The variation of T_c with hole concentration in the new copper oxide superconductors can readily be understood in terms of a peak in the density of states associated with the CuO₂ planes. The data are consistent with either simple phonon-mediated pairing or an indirect excitonic pairing. Effects due to interlayer coupling are considered. The sharp decrease of T_c near half-filling is probable due to strong spin fluctuations.     

Tc in two-zone superconductors with non-magnetic impurities

The two-zone model is used to investigate the influence of nonmagnetic scattering on the superconducting transition temperature. The transition temperature decreases with increasing impurity concentration, and either saturates or goes to zero exponentially at a critical concentration. The type of behaviour is determined by the interaction parameter η∞, which is calculated from the parameters of the model.     

Departures from predicted type II behavior in dirty strong-coupling superconductors

Calorimetric measurements of the Ginsburg-Landau parameters for $\text{Pb}$Sn and $\text{Pb}$Bi alloys show good agreement with the calculations of Rainer and Bergmann for $\text{κ}{}_1\text{(t)}\text{κ}{}_1\text{(1)}$. However, the calculations of Rainer and Usadel for $\text{κ}{}_2\text{(t)}\text{κ}{}_2\text{(1)}$ substantially underestimate the enhancements due to strong-coupling.     

Laser-modulated reflectance of SbSI near Tc

Reflectance modulation spectra of the semiconducting ferroelectric compound SbSI, at wavelengths near the fundamental edge and at temperatures around the phase-transition are reported. Modulation was obtained by the periodical injection of free carriers produced by a laser beam chopped at 10.18 Hz. In order to explain the mechanism of photoreflectance in SbSI, a comparison of the experimental data has been made both with electroreflectance spectra and eith the theoretical curve expected under the assumption of a periodical change of free carriers density.     

Dynamic phases and the peak effect in dirty type II superconductors

We study numerically and experimentally the dynamics of driven vortex matter. Our London-Langevin simulations find that the critical current exhibits a peak both across the Bragg glass to vortex glass transition and across the melting line. The peak is accompanied by a clear crossing of the I-V curves. We report transport measurements on untwinned YBCO crystals, in complete accordance with these findings. At higher drives disorder is averaged to reduced values, and in three dimensions the vortices reorder into a "moving solid." The effect of the disorder can be well represented with a "shaking temperature" which is inversely proportional to the velocity.     

Normal state magnetism of the high Tc cuprate superconductors

Magnetic measurements of various types have played an essential role in establishing the novel normal state characteristics of high transition temperature (T_c) superconductors with T_c > 23 K. Among these materials, the highest T_c's ( 125 K) are exhibited by the layered cuprates. In this paper, the normal state magnetic susceptibilities of the cuprates are reviewed and interpreted in the context of magnetic neutron scattering and other magnetic measurements, using the La_2−xM_xCuO₄-type and YBa₂Cu₃O_6+x-type materials as prototypical examples. The evolution of the magnetism upon doping the insulating antiferromagnetic “parent” compounds with x = 0 to form the high temperature superconductors is described. A recurrent property which differentiates these materials from conventional superconductors is the existence of strong antiferromagnetic correlations in the metallic state on the same sublattice of the structure in which the itinerant carriers reside.     

Diffraction effects in the Josephson tunneling between type II superconductors near Hc2

When the lattice of vortices on one side of a SIS tunneling junction moves with respect to that of the other side, we point out that the Josephson current should oscillate in magnitudes and directions as a function of time. The oscillatory behaviour is caused mainly by the diffraction effects of the variation of the order parameter in the mixed state with vortex motion.     

The effectiveness of different phonon frequencies in enhancing the Tc of superconductors

It is shown that two simple equations for the superconducting transition temperature, both of which give quite accurate values of T_c and practically the same results for the isotope effect, do not agree even qualitatively when used to calculate the effectiveness of different phonon frequencies in enhancing T_c.     

Magnetic impurities in amorphous superconductors:TKondo>Tc

Measurements of upper critical field as a function of temperature and Fe-concentration are reported for the amorphous superconductors ((Mo_.6Ru_.4)_.80G_.20)_1−cFe_c, where G is a glass-former. The linear shapes of the H_c2 vs. T curves near T_c agree well with predictions made by Matsura, Ichinose, and Nagaoka, for T_Kondo > T_c.     

Anomalous dependence of critical magnetic field near Tc of lead-molybdenum chevrel phases

Temperature dependence of critical magnetic field of Pb-ternary molybdenum sulphides is studied. The derivative $\text{?H}{}_{\mathrm{<mtext>c</mtext><mtext>2</mtext>}}\text{?T}$ increases anomalously near T_c. Possible physical mechanisms of this effect are discussed.     

Hall effect in intrinsic type II superconductors near the lower critical field

The Hall angle θ in three V samples (RRR = 80, 120, 140) and two Nb samples (RRR = 57, 66) has been measured in the mixed state in order to elucidate the transport properties in the intrinsic type-II superconductors with intermediate purity.     

Tc enhancement!

The equilibrium critical temperature of a superconducting aluminum strip has been determined with three different methods. The results agree to within 1 mK. By applying microwave radiation superconductivity was maintained up to 57 mK above this critical temperature. These data clearly establish the existense of T_c enhancement.     

Mechanism of high Tc superconductivity and and anti-ferromagnetic order of high Tc oxides

We propose, here, new theory of high T_c superconductivity mechanism. The hole-Cooper pair formation and the Bose condensation of the Cooper pairs occur in the high T_c superconducting oxides such as Bi–Sr–Ca–Cu–O. The atractive interaction is due to the antiferromagnetic order and its fluctuation of CuO₂ plane. Dependence of T_c on the numbers of CuO₂ layers is quantitatively analized.     

Itinerant ferromagnets above Tc

We point out that itinerant ferromagnets differ from Heisenberg ones because the magnetic energy is mainly obtained in the paramagnetic phase. This makes any mean-field theory break down. In order to correct it, one must use the concept of reaction field first introduced by Onsager. We present a theory which takes this into account and permits us to describe in a unified way both the very weak and the pure 3d metallic ferromagnets. In particular we obtain a functional of the magnetization which is valid for the two limits. A consequence of this fact is that the 3d metals behave as very weak ferromagnets close to T_c.     

Quasipartiele model for the quark-gluon plasma: Equation of state near Tc

We test the quark mass dependence implemented in the quasiparticle dispersion relations of our quasiparticle model for the QCD equation of state by comparing with recently available lattice QCD data employing almost physical quark masses. In addition, we emphasize the capability of our model to successfully describe lattice QCD results (or imaginary chemical potential and to analytically continue the latter to real chemical potential.     

一个新的Tc公式

从Eliashberg方程导出了一个适用于λ小的超导体的T_c公式。 关键词：     

Density of states in type-II superconductors in high magnetic fields

Using the Gorkov theory as modified by Eilenberger we derive a consistent calculation scheme for the density of states near the upper critical field. This method applies to arbitrary impurity concentration and becomes in particular simple in the clean limit. Special attention was paid to the effect of anisotropic impurity scattering (p-waves).