Eliashberg function in amorphous superconductors

The conventional approach to tunnelling and critical temperature analysis for amorphous superconductors is discussed. Comparison is made on the effect of structural disorder on the electron-phonon coupling in nearly-free-electron and nearly-localized-electron metals. The results are in good agreement with tunnelling data.     

The fluctuation enhanced conductivity in amorphous superconductors

Considering the effective phonon density of states obtained by tunnel spectroscopic measurements, we conclude that in amorphous metals such as Bi, Ga, and Pb, the electron-phonon collision rate becomes as large as 10¹²/sec at the transition temperature. This is attributed to the collision drag effect which couples low frequency transverse phonons to the electrons. It is shown that such a large collision rate suppresses the Maki contribution to the fluctuation enhanced conductivity.     

Dynamics of quantum vortices in two-dimensional superconductors

The dynamics of rigid vortex translations in two-dimensional arrays of Josephson junctions is shown to be equivalent to the motion of a mass, proportional to the junction capacitance, in a periodic pinning potential. The quantum tunneling of the vortex through the potential barriers is predicted of importance in the existing Nb-arrays at very low temperatures. Above the vortex unbinding temperature there is a plasma resonance of the free vortices leading to an anomaly in the vortex frequency dependent dielectric constant, which could be observed via a radio frequency impedance measurement.     

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.     

Spin orthogonality catastrophe in two-dimensional antiferromagnets and superconductors

We compute the spectral function of a spin S hole injected into a two-dimensional antiferromagnet or superconductor in the vicinity of a magnetic quantum critical point. We show that, near Van Hove singularities, the problem maps onto that of a static vacancy carrying excess spin S. The hole creation operator is characterized by a new boundary anomalous dimension and a vanishing quasiparticle residue at the critical point. We discuss possible relevance to photoemission spectra of cuprate superconductors near the antinodal points.