GINZBURG-LANDAU THEORY OF A D-WAVE SUPERCONDUCTOR WITH MASS ANISOTROPY - PAIRING SYMMETRY AND VORTEX STRUCTURES

YBa2Cu3O7 (YBCO) exhibits a large anisotropy between the a (or y) and b (or x) axes in the CuO2 planes. This anisotropy can be modeled by in troducing an anisotropic mass parameter lambda = m(x)/m(y). Assuming a d-wave pairing interaction together with a repulsive on-site Coulomb interaction, we developed a Ginzburg-Landau theory for a d-wave superc onductor with mass anisotropy in the presence of a magnetic field. We show that the order parameter always has s + d symmetry. The vortex st ructures for lambda = 1 and lambda > 1 have been numerically studied. For high T-c cuprates with tetragonal structure (lambda = 1), the vort ex shows a four-fold symmetry and the vortex lattice may have oblique or triangular structure depending on the strength of the applied magne tic field, temperature, and the other parameters. For YBCO we choose l ambda = 2, the single vortex has an elliptic shape, and the vortex lat tice always shows an oblique structure. All these results are in good agreement with experimental measurements.