  D3 and D7-branes intersecting in 2+1 dimensions give rise at low energies to
N=4 supersymmetric Yang-Mills theory coupled to defect fermions in the
fundamental representation. This theory undergoes a BKT-type phase transition
from a conformal phase to one in which the fermions acquire a non-zero mass
when the 't Hooft coupling of the N=4 SYM exceeds a critical value. To study
this transition, we continue the parameters of the model to a regime where a
gravitational description is valid. We use it to calculate the masses of mesons
and the phase diagram as a function of temperature and chemical potential. We
also comment on the relation of our discussion to the transition from the
non-abelian Coulomb phase to a confining one believed to occur in QCD at a
critical number of flavors.
