Destruction of the Meissner effect in granular high-temperature superconductors

Abstract

We discuss a state of an orbital glass which may exist in granular superconductors. The orbital glass is related to the existence of the special loops of Josephson junctions with positive and negative Josephson couplings. With an odd number of negative couplings on the loop, a spontaneous orbital moment is created. Similar to anyon superconductivity, the new state with orbital moments is characterized by broken fundamental symmetries (C and P). There the orbital paramagnetism coexists with the superconductivity and at small magnetic field and low temperatures the Meissner effect may disappear.