ON THE FOURFOLD SYMMETRY OF H-C2 AND MAGNETIZATION OF D(X(2)-Y(2))-WAVE SUPERCONDUCTORS FOR THE INPLANE MAGNETIC-FIELDS

For the d(x2-y2) superconductors, we investigate the foul-fold symmetr y of the upper critical fields and magnetization related to the torque under the parallel magnetic field to the ab plane of the crystal. We take into account the s-wave order parameter induced from the spatial variation of the d(x2-y2)-wave order parameter. In addition, we invest igate the effects of the shape of the Fermi surface. If the pairing in teraction for the s-wave channel is attractive. the s-wave component c an enhance the above fourfold symmetry. Depending on the structure of the Fermi surface, the fourfold symmetric anisotropy in the ab plane e nhances or suppresses the fourfold symmetric behavior. There is also t he case where the fourfold symmetric anisotropy of in the ab plane cha nges the sign of the fourfold symmetric behavior from that of the isot ropic case.