Anomalous Acoustoelectric Effect in La_0.67Ca_0.33MnO₃ Films

We have studied the acoustoelectric (AE) effect produced by surface acoustic waves (SAW) in a monolithic layered structure, composed of a piezodielectric LiNbO₃ substrate and a La_0.67Ca_0.33MnO₃ film. The experiments unexpectedly revealed in the longitudinal AE effect an anomalous contribution, invariant upon reversal of SAW propagation, which coexists with the ordinary (odd in wave vector) effect. The anomalous effect dominates near the metal-insulator transition, while the ordinary effect prevails at high and low temperatures. We show that the anomalous effect is caused by strong modulation of the film conductivity produced by the SAW elastic deformations.