Splitting instability of a doubly quantized vortex in superfluid Fermi gases

The splitting instability of a doubly quantized vortex in the BEC-BCS crossover of a superfluid Fermi gas is investigated by means of a low-energy effective field theory. Our linear stability analysis and nonequilibrium numerical simulations reveal that the character of the instability drastically changes across the crossover. In the BEC limit, the splitting of the vortex into two singly quantized vortices occurs through the emission of phonons, while such an emission is completely absent in the BCS limit. In the crossover regime, the instability and phonon emission are enhanced and the lifetime of a doubly quantized vortex becomes minimal. The emitted phonon can be observed as a spiraling pattern amplified due to the rotational superradiance, known as a mechanism to carry away energy and angular momentum from a spinning black hole. We also investigate the influence of temperature, population imbalance, and three-dimensional effects.