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 Fermi-liquid 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. d-wave order parameter to surface conditions is not found in traditional a-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 T-c in thin strips of high-T-c superconductors.