P. Lindenfeld

Superconducting coherence in bulk granular metals

Abstract Long-range phase coherence in bulk (three-dimensional) granular metals is governed by a variety of physical mechanisms. We discuss in particular the striking similarities to some behavior observed in discontinuous thin films that has been attributed to the topological ordering associated with the superconducting state in a two-dimensional system.

The metal-insulator transition in La1.85Sr0.15CuO4 with various substitutions for Cu

The authors have determined the concentrations x of Zn, Ga, Fe, and Ni impurities which lead to a metal-insulator transition when substituted for Cu in La1.85Sr0.15CuO4. In each case these values of x are larger than those which are associated with the disappearance of superconductivity.

Superconductivity and the metal-insulator transition in La1.85Sr0.15CuO4.

Abstract Measurements on La 1.85 Sr 0.15 CuO 4 with five different substitutions for the Cu show that the M-I transition occurs in each case at an impurity concentration x MI higher than the value x c at which superconductivity disappears. While x c correlates with the magnitude of the local magnetic moment, we show that the M-I transition is the result of the superposition of the disorder and of the change in carrier concentration as obtained from the Hall effect. On the metallic side the normal-state conductivity changes linearly with √ T over a wide range of temperature. The normal-state conductivity extrapolated to zero temperature exhibits a critical exponent close to one as the M-I transition is approached.

Superconductivity and metal-insulator transition in zinc-substituted La1.85Sr0.15CuO4

When Zn is substituted for Cu in La 1.85 Sr 0.15 CuO 4 , T c goes to zero near 3 at %. The metal-insulator transition occurs at a higher concentration, so that there is a non-superconducting but metallic range of impurity concentration.

Superconductivity near the metal-insulator transition

Abstract Spin-orbit scattering is enhanced in granular aluminum by the addition of small amounts of bismuth. The metal-insulator transition is displaced to larger values of room-temperature resistivity. The superconducting-normal threshold is displaced by an approximately equal amount.