Orbital magnetic moment of a chiral p-wave superconductor

Abstract

The existence and magnitude of a bulk orbital angular momentum of the chiral condensate in the A phase of superfluid helium-3 is a longstanding matter of controversy. The analogous problem in a chiral p-wave superconducting material is the existence of a finite orbital magnetic moment in the bulk. In Sr2RuO4, the existence of such an orbital moment is strongly suggested by experimental evidence for spontaneous time-reversal symmetry breaking (TRSB) in the superconducting state, but the theories disagree on the expected magnitude of this moment. We show that a nonzero orbital magnetization density arises naturally in a realistic band model for Sr2RuO4, and its temperature dependence is qualitatively similar to those of the muon spin rotation and Kerr effect experimental results. The simplest model that leads to the orbital moment requires at least two degenerate atomic orbitals per Ru, which correspond to the Ru dxz and dyz states. This is in contrast to the theories of orbital angular momentum in the isotropic superfluid 3He, or models of orbital moment in Sr2RuO4 which assume only a single band at the Fermi level. The implications of this surprising result are explored.