BOUND-STATES AND JOSEPHSON CURRENT IN MESOSCOPIC S-WAVE SUPERCONDUCTOR-NORMAL-METAL-D-WAVE SUPERCONDUCTOR JUNCTIONS

We have investigated the superconducting phase difference dependence o f Andreev levels and Josephson current through a mesoscopic normal-met al layer in contact with two superconducting electrodes with s-wave an d d-wave pairing symmetry (SsNSd junction). It is shown that, regardle ss of the junction length, due to the sign change of the d-wave order parameter under suitable arrangements, the zero-energy point of Andree v levels for the negative process appears at phi=0. In particular, at zero temperature, the amplitude of the total Josephson current through the point contact SsNSd junction could be enhanced by the sign change of the d-wave order parameter. However, for an SsNSd junction of spec ial length, the amplitude of Josephson current may be suppressed by th is sign change. Moreover, as a special case, the midgap surface states discovered by Hu [Phys. Rev. Leb. 72, 1526 (1994)] are recovered natu rally.