Nonlinear absorption of surface acoustic waves by composite fermions
  Absorption of surface acoustic waves by a two-dimensional electron gas in a perpendicular magnetic field is considered. The structure of such system at the filling factor $\nu$ close to 1/2 can be understood as a gas of {\em composite fermions}. It is shown that the absorption at $\nu =1/2 $ can be strongly nonlinear, while small deviation form 1/2 will restore the linear absorption. Study of nonlinear absorption allows one to determine the force acting upon the composite fermions from the acoustic wave at turning points of their trajectories. 
Joakim Bergli and Yuri Galperin