FLUX CREEP IN JOSEPHSON JUNCTION ARRAYS

In order to analyze the diamagnetic properties of weakly coupled structures in high T(c) ceramic superconductors, the Josephson junction array model is used. We suppose that the coupling is strong enough to allow magnetic flux trapping inside non superconducting regions surrounded by superconducting loops closed by Josephson junctions. We remark that the presence of currents flowing through the junctions has to be taken explicity into account in the Hamiltonian. This description leads to a creep model of the Josephson junction array. Indeed we have: 1) pinning centers generated by non superconducting regions into the loops, 2) pinning potentials determined by fluxon motion barriers due to the Josephson junctions, 3) absence of degeneracy of the states corresponding to a different number of fluxons in the loops, 4) a reduction of the barrier height due to measuring currents or to diamagnetic shielding currents. The last effect is equivalent to the Lorentz force effect in type-II superconductors. In this way we believe that this picture deeply modifies the usual superconducting glass model.