Excess currents larger than the point contact limit in normal-metal/superconducting junctions

7In a point contact NS junction, perfect Andreev reflection occurs over a r ange of voltages equal to the superconducting energy gap, producing an exce ss current of I-exc = (4/3)(2e Delta/h). If the superconductor has a finite width, rather than the infinite width of the point contact, one cannot neg lect superfluid flow inside the superconducting contact. The energy range a vailable for perfect Andreev reflections then becomes larger than the super conducting gap, since superfluid flow alters the dispersion relation inside the finite width superconductor. We find a maximum excess current of appro ximately (7/3)(2e Delta/h) when the width of the superconductor is approxim ately 7/3 times the width of the normal metal. (C) 1999 Academic Press.