  We describe a new phase transition of the bilayer quantum Hall ferromagnet at
filling fraction $\nu = 1$. In the presence of static disorder (modeled by a
periodic potential), bosonic $S=1/2$ spinons can undergo a superfluid-insulator
transition while preserving the ferromagnetic order. The Mott insulating phase
has an emergent U(1) photon, and the transition is between Higgs and Coulomb
phases of this photon. Physical consequences for charge and counterflow
conductivity, and for interlayer tunneling conductance in the presence of
quenched disorder are discussed.
