Model relating superconductive penetration depth and metallurgical phase separation in amorphous La70Cu30

A model is proposed to account for the large increase in the measured penetration depth of superconducting, amorphous La₇₀Cu₃₀ when the specimens are annealed sufficiently long near, but below, the crystallization temperature. It is suggested that a metallurgical phase separation occurs with domain dimensions in the submicrometer range. Penetration depth measurements as a function of temperature in a weak magnetic field are a useful tool to detect changes in phase separation in high-K materials.