CANCELLATION OF QUASI-PARTICLE MASS ENHANCEMENT IN THE CONDUCTANCE OF POINT CONTACTS

The high fraction of Andreev reflections that has been observed in noble-metal point contacts with the high-Tc oxides YBa2Cu3O7 and La2-xSrxCuO4 as well as with the heavy-fermion superconductors UPt3 and URu2Si2 suggests that the boundary condition at the interface involves Fermi velocities without mass-enhancement factors. We show theoretically that this is indeed the case for a self-energy (,k) only weakly dependent on k. A comparison between the velocities derived from point-contact experiments with known values of the fully dressed quasiparticle velocities allows a determination of the mass-enhancement factor. © 1994 The American Physical Society.