ROBUSTNESS OF THE MIDGAP STATES PREDICTED TO EXIST ON A (110)SURFACE OF A D(X2A)-(X2B)-WAVE SUPERCONDUCTOR

It was shown recently that a sizable areal density of midgap states exists on a {110} surface of a dxa2-xb2-wave superconductor [C.-R. Hu, Phys. Rev. Lett. 72, 1526 (1994)]. Here we study how these midgap states are affected if (i) the surface is not exactly {110}; (ii) the crystalline structure is slightly orthorhombic; (iii) and (iv): the order parameter is not a pure d wave, but is s+idxa2-xb2 and dxa2-xb2+idxaxb, respectively. We find that for cases (i) and (ii), the midgap surface states still exist but with reduced areal density. For case (iii), all surface-state energies are found to shift away from midgap to ±Δs. For case (iv), the surface states exist on both {110} and {100} surfaces (and on surfaces of all other orientations) but with a k-dependent energy shift from midgap. © 1994 The American Physical Society.