Vortex lattice structure in a d-wave superconductor with orthorhombic distortion

The vortex lattice structure in an orthorhombic d-wave superconductor under a magnetic field parallel to the c axis is studied near the upper critical field using the phenomenological D-2h symmetric Ginzburg-Landau free-energy density. The equilibrium vortex lattices are commonly body-centered rectangular lattice with no rotation relative to the underlying crystal. At certain temperature which depends on the parameters describing the a-b anisotropy, the flux lattice undergoes a second-order phase transition with the direction of the elongation of the rectangular lattice rotated by 90 degrees (e.g., from the b-axis direction to the a-axis direction). The phase transition temperature is estimated within two microscopic models. [S0163-1829(99)05117-6].