Anomalous first-to-zero sound crossover inLa1−xCaxMnO3

Abstract

The elastic properties of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ $(x\ensuremath{\approx}1∕3)$ are anomalous, particularly in the paramagnetic phase, where values of the longitudinal sound velocity at $\ensuremath{\sim}{10}^{10}\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}$, in the zero-sound regime, are more than 50% larger than those from ultrasound experiments at ${10}^{3}--{10}^{6}\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}$. 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.