Theory of Field-Induced Transition from Node-less to Nodal Pairing in β−PdBi₂

Recent tunneling spectroscopy experiments on tetragonal β−PdBi₂, which has a sizable spin-orbit coupling and multiple pocket-like Fermi surfaces, have detected a magnetic field-induced transition from node-less to nodal superconductivity. Motivated by these findings, we develop a theoretical model, in which superconductivity arises from a nominally repulsive interaction between fermions in different pockets, similar to the case of Fe-pnictides. Within this mechanism, we find that at zero magnetic field, the superconducting state is chiral and node-less p_x±ip_y, where the p-wave component of the interaction comes from form factors associated with the “orbital” content of low-energy excitations. Upon applying an in-plane magnetic field, spin polarization lifts the degeneracy between the two p-wave components of the gap, and above a certain field value the gap becomes a single-component nodal p-wave.