Flux trapping and superconductive glass state in La2CuO4-y:Ba

The mixed copper-oxide superconductors recently discovered are not classical superconductors but have been shown to exhibit some properties of a superconducting glass. The grains in these ceramics are not uniform bulk materials but rather a composition of coupled superconducting clusters. Evidence for the superconducting glass state was first seen in the susceptibility, chi, and magnetic-moment measurements of powder samples of La2CuO4-y:Ba from 1.9 to 35 K in magnetic fields up to 1.5 T. The diamagnetism observed in the zero-field-cooled state was considerably larger than when field cooled. Figure 1(b) shows typical sequences of temperature dependences expected of a glass state. After zero-field cooling the sample and switching on a 0.03-T field, chi is measured at point A. On heating sample, point B on curve 1 is reached. On recooling, a nearly temperature-independent susceptibility is measured. With further heating, point B is passed until point C is reached on curve 1, where on recooling, a temperature-dependent slope smaller than that of curve is followed. On further heating, curve 1 becomes reversible past point D. This same value D is reached by field cooling from 35 K. In field cooling past D, curve 2 is followed reversibly on a time scale of two hours