Most superconductors exhibit spin-singlet pairing within a single band. In multiband systems with strong spin-orbit coupling, more exotic scenarios can emerge, including Cooper pairs between bands with distinct symmetries. Here, we present evidence of the formation of Cooper pairs between spin-nondegenerate helical surface bands in the superconductor $\beta \text{−}{\text{Bi}}_2\mathrm{Pd}$. Scanning tunneling microscopy reveals anisotropic Yu-Shiba-Rusinov (YSR) resonances induced by vanadium impurities, with long-range amplitude modulations attributed to spin-conserving Bogoliubov quasiparticle interference (BQPI). Analysis of BQPI at the subgap YSR energy shows that only a selective subset of normal-state scattering processes contributes to Cooper pair formation, indicating interband mixing. We trace this selectivity to the hybridization of a helical surface band with others via the impurity.

Close

PrevNext

View figure in article

• Impurities in superconductors
• Methods in superconductivity
• Multiband superconductivity
• Pairing mechanisms
• Spin-orbit coupling
• Superconductors
• Scanning tunneling spectroscopy