Ginzburg-Landau theory and vortex structure for a d+s-wave superconductor with orthorhombic distortion

We study microscopically the Ginzburg-Landau (GL) theory of a d+s-wave superconductor with orthorhombic symmetry. The anisotropic pairing interaction due to the orthorhombic distortion leads to a second-order coupling between the s- and d-wave components which is proportional to the anisotropy parameter. This coupling induces a nonvanishing s-wave component even in a uniform system and a relative zero phase between the s- and d-wave components is favored. The ratio of the homogeneous bulk value of the s-wave component to that of the d-wave component decreases linearly as the temperature decreases in the vicinity of Tc. The single vortex structure is studied by solving the GL equations. The asymptotic form of the order parameter for large r is proportional to eif(θ) instead of eiθ where f(θ) is a function of the anisotropy parameter. Near and far away from the vortex core, both s- and d-wave components exhibit a twofold symmetry. As the temperature is sufficiently close to Tc, the s-wave component exhibits almost the same behavior as the d-wave one. From the solution near the vortex core, we give a criterion for the appearance of the s-wave off-center vortices. copyright 1997 The American Physical Society