Collective modes in superconductors near Tc

A phonon-like critical mode is obtained in superconductors near T_c as a result of screening due to electron-lattice ion interaction.     

Density of states in dirty type II superconductors near Tc

We have determined the behavior of the density of states in the mixed state of superconducting alloys for T → T_c. The local density of states tends towards the BCS expression with the order parameter playing the role of the energy gap. The singularities are smeared out by the spatial average. The effective normal core radius of a vortex diverges like $\text{(1 ?}\text{T}\text{T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}$ for T → T_c unlike the coherence length which diverges like $\text{(1 ?}\text{T}\text{T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$.     

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.     

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.     

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.     

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.     

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.     

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 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.     

Collective modes in the loop ordered phase of cuprate superconductors

We show that the two branches of collective modes discovered recently in underdoped cuprates with a large spectral weight are a necessary consequence of the loop-current state. Such a state has been shown in earlier experiments to be consistent with the symmetry of the order parameter competing with superconductivity in four families of cuprates. We also predict a third branch of excitations which cannot be discovered by neutron scattering but may be discovered by other techniques. Using parameters to fit the observed modes, we show that quantum fluctuations change the direction of the effective moments in the ground state to lie at an angle to the c axis as observed in experiments.     

Spin-one color superconductors: Collective modes and effective Lagrangian

We investigate the collective excitations in spin-one color superconductors. We classify the Nambu–Goldstone modes by the pattern of spontaneous symmetry breaking, and then use the Ginzburg–Landau theory to derive their dispersion relations. These soft modes play an important role for the low-energy dynamics of the system such as the transport phenomena and hence are relevant for late-stage evolution of neutron stars. In the case of the color-spin-locking phase, we use a functional technique to obtain the low-energy effective action for the physical Nambu–Goldstone bosons that survive after gauging the color symmetry.     

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.     

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：     

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.     

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.     

Deviation from Kittel's magnetic resonance formula near Tc of CdCr2Se4

Approaching the Curie temperature of the cubic ferromagnet CdCr₂Se₄ from above, the g-factor increasingly shifts from the value predicted by Kittel's formula. In the exchange critical region (susceptibility χ ?1) the g-shift is consistent with δg/g ≈ χ² following from the complex self-energy.     

高Tc超导体的表面微波吸收

测量不同粒度及低真空条件下高T_c超导样品Bi-Pb-Sb-Sr-Ca-Cu-O的非共振微波吸收信号,实验表明,这个对温度和磁场十分敏感的信号还与样品颗粒的大小及氧气氛有关;并经计算证明,信号强度与近表面趋肤深度壳层Meissner态的体积成正比。 关键词：