Cooper Pair Shape in Normal-metal/Superconductor Junctions

TL;DR

This paper reveals that Cooper pairs in normal-metal/superconductor junctions are anisotropic due to quasiparticle interference, challenging the assumption of isotropy from the proximity effect, and proposes an experiment to verify this.

Contribution

It demonstrates that the pairing function in a normal metal is anisotropic, contrary to previous assumptions, and introduces a method to detect this via angle-resolved quasiparticle density of states.

Findings

Cooper pairs in NS junctions are anisotropic due to quasiparticle interference.

Calculated angle-resolved quasiparticle density of states reflects the anisotropic pairing.

Proposed magneto-tunneling spectroscopy experiment to confirm anisotropy.

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 magneto-tunneling spectroscopy experiment which could confirm our predictions.