Surface superconductivity and anomalous flux jumps in organic superconductors

A model is proposed to explain the recently reported anomalous flux jumps in the organic superconductor K-(BEDT-TTF)(2)Cu(N(CN)(2))Br. The model is based on the nature of the soft lattice in the organic materials and the plastic energy of interaction between dislocation fields and defects. During the cooling processes, point defects will be set in motion when the static interaction energy between dislocation field and a defect exceeds the plastic energy of the lattice. The motion of defects leads to breaking up of the flux line lattice and the onset of an inhomogeneous plastic flow. This motion will contribute to the formation of regions in the elastic medium where defects may form chunks or domains. These domains are determined by the stress field and are characterized by a length scale of the order of the lattice constant no. At each domain and within distances of the order of no, the time average magnetization due to surface superconductivity at the edge of each defect in that domain are correlated. As a result, the magnetic moments of a defect or chunk of defects will have extra contributions to the magnetization of the sample and, consequently, the observed rapid fluctuation in the magnetization, M. The predictions of the model are in excellent agreement with the recently reported experimental measurements. (C) 2001 Elsevier Science B.V. All rights reserved.