The first direct spectral observation of critical incoherent quasielastic neutron scattering is reported. This result has been obtained by a combination of time-of-flight and high-resolution backscattering spectrometers with use of a single crystal of selectively deuterated p-terphenyl in the vicinity of the order-disorder phase transition. The relation of the incoherent-scattering results to critical coherent neutron scattering is discussed.

• Received 22 July 1985

DOI:https://doi.org/10.1103/PhysRevLett.56.347