  We study the holographic dual of a (2+1)-dimensional s-wave superfluid that
breaks an abelian U(1) x U(1) global symmetry group to the diagonal U(1)_V. The
model is inspired by Sen's tachyonic action, and the operator that condenses
transforms in the bifundamental representation of the symmetry group. We focus
on two configurations: the first one describes a marginal operator, and the
phase diagram at finite temperature contains a first or a second order phase
transition, depending on the parameters that determine the theory. In the
second model the operator is relevant and the finite temperature transitions
are always second order. In the latter case the conductivity for the current
associated to the broken symmetry shows quasiparticle excitations at low
temperatures, with mass given by the width of the superconducting gap. The
suppression of spectral weight at low frequencies is also observed in the
conductivity associated to the conserved symmetry, for which the DC value
decreases as the temperature is reduced.
