An anomalous acoustoelectric effect

An anomalous acoustoelectric effect has been discovered in a manganite thin film by a collaboration of physicists in Russia, Poland, and Ukraine. When an acoustic wave propagates along an electrically conducting surface, it can drag electric charge along with it if there is strong coupling between phonons and electrons. This is known as the acoustoelectric (AE) effect. Manganites are known to show a rich variety of strongly interrelated magnetic, structural, and electrical properties. The researchers grew a manganite thin film atop a piezoelectric lithium-niobium-oxygen substrate, on which they then launched a surface acoustic wave (SAW). They unexpectedly found that a component of the AE current did not reverse when the SAW traveled in the opposite direction. The physicists discovered that the anomalous AE current was related to the strong pressure dependence of the manganite film’s conductivity. The total AE current peaked at a temperature near the metal-insulator transition, at which the anomalous effect dominated. At higher and lower temperatures, the ordinary AE effect prevailed. (Y. Ilisavskii et al., Phys. Rev. Lett. 87, 146602, 2001 http://dx.doi.org/10.1103/PhysRevLett.87.146602 .)