Intrinsic finite-energy Cooper pairing in j=3/2 superconductors

Abstract

We show that Cooper pairing can occur intrinsically away from the Fermi surface in j=3/2 superconductors with strong spin-orbit coupling and equally curved bands in the normal state. In contrast to conventional pairing between spin-1/2 electrons, we derive that pairing can happen between interband electrons having different magnetic quantum numbers, for instance, mj=1/2 and mj=3/2. Such superconducting correlations manifest themselves by a pair of indirect gaplike structures at finite excitation energies. An observable signature of this exotic pairing is the emergence of a pair of symmetric superconducting coherence peaks in the density of states at finite energies. Moreover, the angular-momentum-resolved density of states in the presence of a perturbative Zeeman field reflects the mj composition of the Cooper pairs. We argue that such finite-energy pairing is a generic feature of j=3/2 superconductors, both in the presence and absence of inversion symmetry.