Anomalous superconducting proximity effect of planar Pb-RhPb2 heterojunctions in the clean limit

TL;DR

This study demonstrates an anomalously long-range superconducting proximity effect in atomically sharp Pb-RhPb2 heterojunctions, revealing unusual pairing gap modifications and symmetry breaking in the clean limit, with implications for topological superconductivity.

Contribution

It reports the first spectroscopic imaging of the proximity effect in clean superconductor-superconductor heterojunctions, showing long-range effects and symmetry breaking.

Findings

Unusual modifications in the pairing gap structure extend beyond the coherence length.

Long-range proximity effect breaks the rotational symmetry of Cooper pairs.

Deformation of Abrikosov vortex cores observed in the heterojunctions.

Abstract

Interest in superconducting proximity effect has been revived by the exploitation of Andreev states and by the possible emergence of Majorana bound states at the interface. Spectroscopy of these states has been so far restricted to just a handful of superconductor-metal systems in the diffusion regime, whereas reports in otherwise clean superconductor-superconductor heterojunctions are scarce. Here, we realize molecular beam epitaxy growth of atomically sharp planar heterojunctions between Pb and a topological superconductor candidate RhPb2 that allows us to spectroscopically image the proximity effect in the clean limit. The measured energy spectra of RhPb2 vary with the spatial separation from proximal Pb, and exhibit unusual modifications in the pairing gap structure and size that extend over a distance far beyond the coherence length. This anomalously long-range proximity (LRP) effect breaks the rotational symmetry of Cooper pair potential in real space and largely deforms the Abrikosov vortex cores. Our work opens promising avenues for fundamental studies of the Andreev physics and extraordinary states in clean superconducting heterojunctions.