  We use time-dependent Hartree Fock approximation to study the collective mode
spectra of nu=2 quantum Hall bilayers in tilted magnetic field allowing for
charge imbalance as well as tunneling between the two layers. In a previous
companion paper to this work, we studied the zero temperature global phase
diagram of this system which was found to include a symmetric and ferromagnetic
phases as well as a first order transition between two canted phases with
spontaneously broken U(1) symmetry. We further found that this first order
transition line ends in a quantum critical point within the canted region. In
the current work, we study the excitation spectra of all of these phases and
pay particular attention to the behavior of the collective modes near the phase
transitions. We find, most interestingly, that the first order transition
between the two canted phases is signaled by a near softening of a magnetoroton
minimum. Many of the collective mode features explored here should be
accessible experimentally in light scattering experiments.

Mesoscale and Nanoscale Physics