Anomalous Acoustoelectric Effect in ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ Films

We have studied the acoustoelectric (AE) effect produced by surface acoustic waves (SAW) in a monolithic layered structure, composed of a piezodielectric ${\mathrm{LiNbO}}_3$ substrate and a ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ 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.