Acoustic anomalies in Jahn-Teller coupled systems

Abstract
The theory of the coupling between the acoustic phonon modes and a two level electronic system is studied with reference to the Jahn-Teller phase transition in DyVO4. The connection with the macroscopic strain is discussed, and expressions given for the coupled mode frequencies and the elastic constants. The model also accounts satisfactorily for the temperature variation of the elastic constant of KDP near the 122 K ferroelectric phase transition.