LOCAL-DENSITY OF STATES ON ROUGH SURFACES OF D(X(2)-Y(2))-WAVE SUPERCONDUCTORS

The spatial variations of the local density of states (LDOS) on the su rface of d(x2-y2)-wave superconductors are calculated using an extende d Hubbard model. Our model has the ability to treat the surface geomet ry with atomic-scale roughness, and gives realistic results beyond tho se based on the quasiclassical theory. The spatial variation of the LD OS is obtained for various types of surface geometries using a self-co nsistently determined pair potential. As surface bound states are pecu liar to d-wave superconductors, we pay attention to the appearance of zero-energy states (ZES's). For a flat surface, the formation of a ZES on a [110] surface and the lack of one on a [100] surface is obtained , which is consistent with the results of the quasiclassical theory. H owever, the LDOS shows abundant spatial dependence when the surfaces h ave roughness. The appearance of a ZES on nominal [100] surfaces and i ts disappearance on nominal [110] surfaces are obtained depending on g eometry. The calculations explain the origin of various spectra observ ed by tunneling spectroscopy on high-T-c superconductors.