ELECTRONIC STATES ON A TWIN BOUNDARY OF A D-WAVE SUPERCONDUCTOR

We show that an induced s-wave harmonic in the superconducting gap of an orthorhombic d(x2-y2) superconductor strongly affects the excitatio n spectrum near a twinning plane. In particular, it yields bound state s of zero energy with areal density proportional to the relative weigh t of the s-wave component. An unusual scattering process responsible f or the thermal conductivity across the twin boundary at low temperatur es is also identified.