Hypersound Observations of Glass Fluctuations

Abstract

Correlations of fourth order in polarization fluctuations, the quantity whose ordering is frustrated, are observed in a structural glass via strictive coupling to sound. The results were obtained on a ${\mathrm{Rb}}_{1-x}{\left(\mathrm{N}{\mathrm{H}}_4\right)}_x{\mathrm{H}}_2\mathrm{P}{\mathrm{O}}_4$ crystal with Brillouin scattering. The existence of an Edwards-Anderson order parameter much above Vogel-Fulcher freezing is revealed. This suggests that the observed susceptibility slowing-down might, in many glasses, be controlled by a much slower hidden competing network.