Exporting superconductivity across the gap: Proximity effect for semiconductor valence-band states due to contact with a simple-metal superconductor

Abstract

The proximity effect refers to the phenomenon whereby superconducting properties are induced in a normal conductor that is in contact with an intrinsically superconducting material. In particular, the combination of nano-structured semiconductors with bulk superconductors is of interest because these systems can host unconventional electronic excitations such as Majorana fermions when the semiconductor's charge carriers are subject to a large spin-orbit coupling. The latter requirement generally favors the use of hole-doped semiconductors. On the other hand, basic symmetry considerations imply that states from typical simple-metal superconductors will predominantly couple to a semiconductor's conduction-band states and, therefore, in the first instance generate a proximity effect for band electrons rather than holes. In this article, we show how the superconducting correlations in the conduction band are transferred also to hole states in the valence band by virtue of inter-band coupling. A general theory of the superconducting proximity effect for bulk and low-dimensional hole systems is presented. The interplay of inter-band coupling and quantum confinement is found to result in unusual wave-vector dependencies of the induced superconducting gap parameters. One particularly appealing consequence is the density tunability of the proximity effect in hole quantum wells and nanowires, which creates new possibilities for manipulating the transition to nontrivial topological phases in these systems.

10 pages, 3 figures, RevTex 4.1, v2: now showing nanowire results for InAs (instead of GaAs in v1), to appear in Phys. Rev. B

References in corpus (10)

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• Suppression of Coulomb exchange energy in quasi-two-dimensional hole systems
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Cited by in corpus (11)

• Pairing of j=3/2 fermions in half-Heusler superconductors
• Majorana Fermions in Ge/Si Hole Nanowires
• Light-Hole Gate-Defined Spin-Orbit Qubit
• Microscopic analysis of proximity-induced superconductivity and metallization effects in superconductor-germanium hole nanowires
• Germanium-based hybrid semiconductor-superconductor topological quantum computing platforms: Disorder effects
• Anisotropic RKKY interactions mediated by $j=3/2$ quasiparticles in half-Heusler topological semimetal
• InP/GaSb core-shell nanowires: a novel hole-based platform with strong spin-orbit coupling for full-shell hybrid devices
• Light-hole spin confined in germanium
• Superconducting Proximity Effect in Two-Dimensional Hole Gases
• Theory of superconducting proximity effect in hole-based hybrid semiconductor-superconductor devices
• Emergence of a condensate with finite-energy Cooper pairing in hybrid exciton/superconductor systems