Andreev reflection spectroscopy in strongly paired superconductors

Abstract

Motivated by recent experiments on low-carrier-density superconductors, including twisted multilayer graphene, we study signatures of the BCS to BEC evolution in Andreev reflection spectroscopy. We establish that in a standard quantum point contact geometry, Andreev reflection in a BEC superconductor is unable to mediate a zero-bias conductance beyond $e^2/h$ per lead channel. This bound is shown to result from a duality that links the sub-gap conductance of BCS and BEC superconductors. We then demonstrate that sharp signatures of BEC superconductivity, including perfect Andreev reflection, can be recovered by tunneling through a suitably designed potential well. We propose various tunneling spectroscopy setups to experimentally probe this recovery.

13 pages, 8 figures

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Cited by in corpus (9)

• Andreev reflection at the altermagnet-superconductor interface
• Junctions and superconducting symmetry in twisted bilayer graphene
• Nonreciprocal superconductivity
• Approximate symmetries, insulators, and superconductivity in continuum-model description of twisted WSe${}_2$
• Andreev reflection in normal metal/charge-4e superconductor junctions
• Probing superconductivity with tunneling spectroscopy in rhombohedral graphene
• Topological two-band electron-hole superconductors with $d$-wave symmetry: Absence of Dirac quasiparticle annihilation in magic-angle twisted trilayer graphene
• Majorana fermions in Kitaev chains side-coupled to normal metals
• SNS Junctions along the BCS-BEC Crossover