Brillouin scattering, ultrasonic and theoretical studies of acoustic anomalies in crystals showing Jahn-Teller phase transitions

Abstract

DyVO4 and TbVO4 undergo a Jahn-Teller induced crystallographic phase change at 14 and 34 K respectively, and elastic constants of these materials behave anomalously at the transition temperature TD. Brillouin scattering measurements on DyVO4 show that the elastic constant (c11 - c12) falls to zero at TD. The electron lattice interaction which drives the transition in this material is predominantly of short range and a cluster theory is used to interpret the measurements. The elastic constant c66 of TbVO4 also has an anomaly. It falls to zero at TD when measured at ultrasonic frequencies but only falls to a finite value when measured at the higher frequencies used in Brillouin scattering. This frequency dependence of the elastic constants is explained using both thermodynamic and microscopic theories.