Neutral Collective Excitations in Striped Hall States
  In the striped Hall state, a magnetic translation in one direction is spontaneously broken to the discrete translation. The spectrum of the neutral collective excitation is obtained in the single mode approximation at half-filled third and fourth Landau levels. The spectrum is anisotropic and has a multiple line node structure. In one direction, the spectrum resembles the liquid Helium spectrum with the phonon and roton minimum. 
N. Maeda, T. Aoyama, Y. Ishizuka, and K. Ishikawa