Dynamical Kohn Anomaly in Surface Acoustic Wave Response in Quantum Hall Systems Near $\nu =1\mathrm{/}2$

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 $\nu =1\mathrm{/}2$. Kinks appear in the velocity shift $Deltas\mathrm{/}s$ and attenuation coefficient $\mathrm{\Gamma }$. The effect is considerably enhanced under periodic modulation and should be observable.