  We theoretically investigate superfluidity in a strongly interacting Fermi
gas confined to two dimensions at finite temperature. Using a Gaussian pair
fluctuation theory in the superfluid phase, we calculate the superfluid density
and determine the critical temperature and chemical potential at the
Berezinskii-Kosterlitz-Thouless transition. We propose that the transition can
be unambiguously demonstrated in cold-atom experiments by stirring the
superfluid Fermi gas using a red detuned laser beam, to identify the
characteristic jump in the local Landau critical velocity at the
superfluid-normal interface, as the laser beam moves across the cloud.
