Physical Review Letters 135, 136201 (2025)
Authors: Javier Zaldívar , Jon Ortuzar , Miguel Alvarado, Stefano Trivini , Julie Baumard,
Carmen Rubio-Verdú, Edwin Herrera, Hermann Suderow, Alfredo Levy Yeyati,
F. Sebastian Bergeret, and Jose Ignacio Pascual
Abstract: 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 β-Bi2Pd. 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.
