SUPERCONDUCTIVITY AND THE METAL-INSULATOR-TRANSITION IN LA1.85SR0.15CUO4

Measurements on La1.85Sr0.15CuO4 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 square-root 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.