ANDREEV REFLECTION ENHANCED AHARONOV-BOHM OSCILLATIONS IN CONDUCTANCEOF A MESOSCOPIC NORMAL-METAL RING CONNECTED TO NORMAL AND SUPERCONDUCTING LEADS

We investigate the conductance through an Aharonov-Bohm normal metal r ing connected to normal and superconducting leads. It is shown that, d ue to the Andreev reflection at the normal superconducting phase bound ary, the conductance maxima could be enhanced to be twice as large as that for the ring connected with normal conducting leads. The voltage bias may suppress this conductance enhancement. However: the periodici ty of the oscillating conductance in flux is not altered by the presen ce of the superconducting contact. The discussion is also extended to include the impurity scattering effect and the multichannel case. Quit e interestingly, the period halving could be induced by the impurity s cattering even in one-dimensional normal superconducting hybrid struct ures.