Dynamical Kohn Anomaly in Surface Acoustic Wave Response in Quantum Hall   Systems Near $\nu = 1/2$
  The dynamical analog of the Kohn Anomaly image of the Fermi Surface is demonstrated for the response functions to the surface acoustic waves in Quantum Hall Systems near $\nu = 1/2$. Kinks appear in the velocity shift $Delta s/s$ and attenuation coefficient $\Gamma$. The effect is considerably enhanced under periodic modulation and should be observable. 
Nataliya A.Zimbovskaya and Joseph L. Birman