Multiphase superconductivity in PdBi2

TL;DR

This study uncovers a magnetic-field-induced phase transition in PdBi2, shifting from conventional to unconventional superconductivity, likely driven by spin polarization and spin-momentum locking, revealing complex multiphase behavior in this layered superconductor.

Contribution

It demonstrates a field-driven transition from s-wave to nodal pairing in PdBi2, highlighting the role of spin-orbit coupling and broken inversion symmetry in unconventional superconductivity.

Findings

Discontinuous change in superconducting properties with in-plane magnetic field.

Evidence of transition from s-wave to nodal pairing.

Theoretical support for spin polarization and spin-momentum locking effects.

Abstract

Unconventional superconductivity, where electron pairing does not involve electron-phonon interactions, is often attributed to magnetic correlations in a material. Well known examples include high-T_c cuprates and uranium-based heavy fermion superconductors. Less explored are unconventional superconductors with strong spin-orbit coupling, where interactions between spin-polarised electrons and external magnetic field can result in multiple superconducting phases and field-induced transitions between them, a rare phenomenon in the superconducting state. Here we report a magnetic-field driven phase transition in \beta-PdBi2, a layered non-magnetic superconductor. Our tunnelling spectroscopy on thin PdBi2 monocrystals incorporated in planar superconductor-insulator-normal metal junctions reveals a marked discontinuity in the superconducting properties with increasing in-plane field, which is consistent with a transition from conventional (s-wave) to nodal pairing. Our theoretical analysis suggests that this phase transition may arise from spin polarisation and spin-momentum locking caused by locally broken inversion symmetry, with p-wave pairing becoming energetically favourable in high fields. Our findings also reconcile earlier predictions of unconventional multigap superconductivity in \beta-PdBi2 with previous experiments where only a single s-wave gap could be detected.