Photon energy absorption rate of a striped Hall gas
  Using symmetries of the current correlation function, we analyze the frequency dependence of the photon energy absorption rate of a striped Hall gas. Since the magnetic translational symmetry is spontaneously broken in the striped Hall gas, a Nambu-Goldstone (NG) mode appears. It is shown that the NG mode causes a sharp absorption at the zero energy in the long wavelength limit by using the single mode approximation. The photon energy absorption rate at the NG mode frequency strongly depends on the direction of the wave number vector. Whereas, the absorption rate at the cyclotron frequency does not depend on the direction of the wave number vector in the long wavelength limit. The cyclotron resonance is not affected in the striped Hall gas. Our result supplements the Kohn's theorem in the system of the NG mode. 
Y. Ishizuka, T. Aoyama, N. Maeda and K. Ishikawa