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 ν close to 1/2 can be understood as a gas of composite fermions. It is shown that the absorption at ν = 1/2 can be strongly nonlinear, while small deviation form 1/2 will restore the linear absorption. The 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. Introduction. – The interaction with surface acoustic waves (SAW) is an important tool in the study of two-dimensional electron gases (2DEG) in various regimes [1], in particular, under conditions of the fractional quantum Hall effect [2, 3]. As is well known, the twodimensional electron system exhibits a metallic phase in strong magnetic fields, near the half-filled Landau level, ν = 1/2. This phase has been understood as a gas of so-called composite fermions (CFs). This concept formulated in the framework of the Chern-Simons theory [4] has appeared successful to explain the acoustic properties of 2DEG [5–7] and to extract quantitative information about CFs’ trajectories. So far, both experimental and theoretical studies have concentrated on the linear response regime, which is valid for low sound intensities. On the other hand, a very peculiar nonlinear response of 3DEG to acoustic waves (AW) has been predicted [8] and experimentally observed in InSb [9] and in Ga [10]. A striking feature of this nonlinear response is its anomalous sensitivity to an external magnetic field [11]. In fact, the nonlinear response appears suppressed by so weak a magnetic field that does not effect linear absorption at all [10]. The theory of nonlinear response in external magnetic field has been elaborated in [12,13], a comprehensive review is given in [14]. What is important is that an external magnetic field provides an intrinsic scale to measure the force acting upon electrons from the AW. It is therefore natural to investigate whether the nonlinear effects observed for electrons are also present in the two-dimensional CF liquid, and what new information they provide. This is the aim of the present paper. (∗) E-mail: [email protected]