Shape of Cooper pairs in a normal-metal/superconductor junction

Abstract

In $s$-wave superconductors the Cooper pair wave function is isotropic in momentum space. This property may also be expected for Cooper pairs entering a normal metal from a superconductor due to the proximity effect. We show, however, that such a deduction is incorrect and the pairing function in a normal metal is surprisingly anisotropic because of quasiparticle interference. We calculate angle-resolved quasiparticle density of states in NS bilayers which reflects such anisotropic shape of the pairing function. We also propose a magnetotunneling spectroscopy experiment which could confirm our predictions.