Gapped optical excitations from gapless phases: imperfect nesting in   unconventional density waves
  We consider the effect of imperfect nesting in quasi-one-dimensional unconventional density waves in the case, when the imperfect nesting and the gap depends on the same wavevector component.   The phase diagram is very similar to that in a conventional density wave. The density of states is highly asymmetric with respect to the Fermi energy.   The optical conductivity at T=0 remains unchanged for small deviations from perfect nesting. For higher imperfect nesting parameter, an optical gap opens, and considerable amount of spectral weight is transferred to higher frequencies. This makes the optical response of our system very similar to that of a conventional density wave. Qualitatively similar results are expected in d-density waves. 
Bal\'azs D\'ora, Andr\'as V\'anyolos, Kazumi Maki, Attila Virosztek