Gaplessness and properties of layered superconductors: Application to high-Tc cuprates

Magnetic scattering effects in two-band superconductor: the ferromagnetic dopants in MgB₂

This paper demonstrates the magnetic scattering effects on the electron-phonon interaction in two-band superconductors based on the transition-metal-doped MgB₂ to clarify the effects of magnetic dopants on multi-band superconductivity. The phonon properties of polycrystalline Mg(1-x)M(x)B₂ (M = Fe, Ni and Co), with x up to 0.05, were studied, with the investigation based on the normal state Raman spectra, especially the variation of the E(2g) mode. The magnetic scattering effect of Fe is much weaker than that of Mn in MgB₂, while it is stronger than that of Ni. The weak magnetic scattering effects are responsible for the superconducting behaviors of Mg(1 - x)Fe(x)B₂ and Mg(1 - x)Ni(x)B₂. Co shows almost no magnetic scattering effects on the superconductivity, while the depression of the critical temperature, T(c), in Mg(1 - x)Co(x)B₂ is attributed to the phonon behavior and is independent of the ferromagnetic nature of cobalt.

A possible mechanism for evading temperature quantum decoherence in living matter by feshbach resonance

A new possible scenario for the origin of the molecular collective behaviour associated with the emergence of living matter is presented. We propose that the transition from a non-living to a living cell could be mapped to a quantum transition to a coherent entanglement of condensates, like in a multigap BCS superconductor. Here the decoherence-evading qualities at high temperature are based on the Feshbach resonance that has been recently proposed as the driving mechanism for high T_c superconductors. Finally we discuss how the proximity to a particular critical point is relevant to the emergence of coherence in the living cell.

Mixed state of a dirty two-band superconductor: application to MgB2

We investigate the vortex state in a two-band superconductor with strong intraband and weak interband electronic scattering rates. Coupled Usadel equations are solved numerically, and the distributions of the pair potentials and local densities of states are calculated for two bands at different values of magnetic fields. The existence of two distinct length scales corresponding to different bands is demonstrated. The results provide qualitative interpretation of recent scanning tunneling microscopy experiments on vortex structure imaging in MgB2.

SOME CHEMICAL AND STRUCTURAL EFFECTS ON THE PROPERTIES OF HIGH-Tc SUPERCONDUCTORS

▪ Abstract  The history of superconductivity, including superconductivity in the high-Tc cuprates, is reviewed very briefly, and the differences between conventional superconductors and the high-Tc cuprates are summarized. The basic crystal structures of the major series of high-Tc cuprates are described and compared. The relation of structures to superconducting properties is reviewed with an emphasis on the orthorhombic-tetragonal transition in (La2−x Srx)CuO4; the corresponding transition, and also the transition to the low-temperature tetragonal phase in (La2−xBax)CuO4; and the effects of oxygen vacancies, oxygen-vacancy ordering, frozen-in disorder, and occupation of the off-chain O(5) sites in YBa2Cu3O7−δ. The effects of chemical substitutions of lanthanide elements on the La/Sr sites in (La2−xSrx)CuO4 and on the Y sites in YBa2Cu3O7−δ, and of 3d elements and sp elements on the Cu sites in both systems are reviewed. The difference between the effects of the lanthanide substitutions, particularly Pr, in the two systems are considered. Major properties of the Bi-, Tl-, and Hg-cuprates, are described briefly. A comparison of the high-Tc cuprates with noncuprate oxide superconductors is given.