Influence of surface roughness on subdominant pairing in d‐wave superconductors

We study a d‐wave superconductor with dominant d x 2‐y 2 ‐wave order parameter and subdominant pairing in either the s‐ or the dxy‐wave channel near a surface. In particular we analyze the influence of surface roughness on the mixed order parameter which may break the time‐reversal symmetry. We find that the subdominant component is suppressed by the roughness independent of its pairing symmetry; for very rough surfaces the subdominant component may even vanish completely. Additionally we discuss a possible real‐valued admixture which counteracts the suppression of the d x 2‐y 2 ‐wave order parameter at the surface.