Orbital Angular Momentum and Spectral Flow in Two-Dimensional Chiral Superfluids

We study the orbital angular momentum (OAM) L_z in two-dimensional chiral (p_x+i p_y)^ν-wave superfluids (SFs) of N fermions on a disk at zero temperature, in terms of spectral asymmetry and spectral flow. It is shown that L_z=ν N /2 for any integer ν , in the Bose-Einstein condensation regime. In contrast, in the BCS limit, while the OAM is L_z=N /2 for the p +i p -wave SF, for chiral SFs with ν ≥2 , the OAM is remarkably suppressed as L_z=N ×O (Δ₀/ɛ_F)≪N , where Δ₀ is the gap amplitude and ɛ_F is the Fermi energy. We demonstrate that the difference between the p +i p -wave SF and the other chiral SFs in the BCS regimes originates from the nature of edge modes and related depairing effects.