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 a t the filling factor v close to 1/2 can be understood as a gas of composite fermions. It is shown that the absorption at v = 1/2 can be strongly nonli near, while small deviation form 1/2 will restore the linear absorption. Th e study of nonlinear absorption allows one to determine the force acting up on the composite fermions from the acoustic wave at turning points of their trajectories.