Surface boundary conditions for the Ginzburg-Landau theory of d-wave superconductors.

We calculate de Gennes’ extrapolation length for a d-wave superconductor near a surface within Fermiliquid theory. The extrapolation length depends critically on the orientation of the surface relative to the crystal axes and on the surface roughness. This sensitivity of the boundary conditions for a d-wave order parameter to surface conditions is not found in traditional s-wave superconductors, and is a signature of anisotropic pairing with a changing sign of the order parameter along the Fermi surface. de Gennes’ method is used to calculate the reduction of Tc in thin strips of high-Tc superconductors.