Anomalous first-to-zero sound crossover in La1-x Cax Mn O3

The elastic properties of La1-x Cax Mn O3 (x≈1 3) are anomalous, particularly in the paramagnetic phase, where values of the longitudinal sound velocity at ∼ 1010 Hz, in the zero-sound regime, are more than 50% larger than those from ultrasound experiments at 103 - 106 Hz. Such a behavior, indicative of coupling to relaxation processes, is similar to that of liquids and soft viscoelastic matter, but quite unusual for a hard solid. These results suggest that the physics of phase separation in manganites is more complex than that of a stationary mixture of competing phases.