Subgap in the Edge States of Two-Dimensional Chiral Superconductor with Rough Surface

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We discuss the rough surface effects on a two-dimensional chiral k_{x}+\mathrm{i}k_{y} superconductor. The atomic scale roughness at the surface is considered using the random S matrix model. The roughness effects on the self-consistent order parameter, surface mass current, and surface density of states are studied using the quasi-classical theory. We find that the surface mass current is suppressed by the surface roughness. The surface density of states shows quite a similar behavior to that of the superfluid 3He B phase. When the surface is specular, the surface Andreev bound states form a band that fills the bulk energy gap \Delta_{\text{bulk}}. When the surface becomes diffusive, there occurs a sharp upper edge of the surface bound states band and there opens a subgap between the edge and the bulk energy gap. We show that this subgap is induced by the repulsion between the surface bound states and the propagating Bogoliubov quasi-particles through the second order process of roughness.
2011-11-15