Multiphase superconductivity in PdBi2.

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 β-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 β-PdBi₂ with previous experiments where only a single s-wave gap could be detected. β-PdBi2 superconducting properties have been known about since the 1950s, with various works since then indicating the possibility of multiple superconducting gaps and unconventional superconductivity. However, so far only a single gap s-wave superconductivity was detected. Here, using tunnelling spectroscopy under an applied magnetic field, Powell et al observe a transition from s-wave to nodal pairing. [ABSTRACT FROM AUTHOR]