Collective Pinning of a Flux-Line Lattice with Screw Dislocations

The energy of screw dislocations of a flux-line lattice in Type-II superconductors is calculated taking account of dispersion of the tilt modulus. On the basis of this calculation, the collective-pinning theory for the plastic case, proposed by Mullock and Evetts, leads to correlation lengths of a flux-line lattice much shorter than that for the elastic case leads, and much better theoretical fits to experimental results in Nb₃Ge and 2H-NbSe_2–xS_xare obtained. Furthermore, the intermediate state between three-dimensional disorder and two-dimensional disorder in a flux-line lattice is predicted when the screw dislocations trigger the dimensional crossover.