Multiply quantized vortices in fermionic superfluids: angular momentum, unpaired fermions, and spectral asymmetry

摘要

We compute the orbital angular momentum $L_z$ of an s-wave paired superfluidin the presence of an axisymmetric multiply quantized vortex. For vortices withwinding number $|k| > 1$, we find that in the weak-pairing BCS regime $L_z$ issignificantly reduced from its value $\hbar N k/2$ in the Bose-Einsteincondensation (BEC) regime, where $N$ is the total number of fermions. Thisdeviation results from the presence of unpaired fermions in the BCS groundstate, which arise as a consequence of spectral flow along the vortex sub-gapstates. We support our results analytically and numerically by solving theBogoliubov-de-Gennes equations within the weak-pairing BCS regime.