JOSEPHSON-COUPLED LAYERED SUPERCONDUCTORS WITH 2 ORDER PARAMETERS .2.LOWER CRITICAL MAGNETIC-FIELD

A model for high-T(c) oxides, consisting of Josephson-coupled supercon ducting layers with both intra- and interlayer pairings, is used to st udy the anomalous positive curvature in the temperature dependence of the lower critical magnetic field, H(c1)(T). An equilibrium distributi on of magnetic fields in a single vortex is calculated for magnetic fi eld parallel and perpendicular to the superconducting layers. By using this distribution the lower critical field H(c1) is obtained. For Jos ephson-coupled layered superconductors with only intralayer pairing, t he cross section of the single vortex parallel to the layers is known to have an elliptic form. The existence of two order parameters in our model gives rise to an additional anisotropy in the distribution of t he magnetic field in a single vortex. The results obtained for H(c1) m ake it possible to understand the experimentally observed anomalous en hancement of H(c1) at low temperatures in YBa2Cu3O7, as well as in Tl- and Bi-based superconductors.