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

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Abstract
YBa 2 Cu 3 O 7 (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 introducing an anisotropic mass parameter λ = mx /my. Assuming a d-wave pairing interaction together with a repulsive on-site Coulomb interaction, we developed a Ginzburg–Landau theory for a d-wave superconductor with mass anisotropy in the presence of a magnetic field. We show that the order parameter always has s + d symmetry. The vortex structures for λ = 1 and λ > 1 have been numerically studied. For high T c cuprates with tetragonal structure (λ = 1), the vortex shows a four-fold symmetry and the vortex lattice may have oblique or triangular structure depending on the strength of the applied magnetic field, temperature, and the other parameters. For YBCO we choose λ = 2, the single vortex has an elliptic shape, and the vortex lattice always shows an oblique structure. All these results are in good agreement with experimental measurements.

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