Diffuse intensity from phonon noise in inelastic neutron scattering

Atomic vibrational dynamics in cuprite ${\mathrm{Cu}}_{2}\mathrm{O}$ was studied by inelastic neutron scattering and molecular-dynamics (MD) simulations from 10 K to 900 K. At 300 K, a diffuse inelastic intensity (DII) appeared in the phonon dispersions, and dominated the spectral intensity at higher temperatures. Classical MD simulations with a machine-learning interatomic potential reproduced general features of the DII. Better agreement with experiment was obtained with the addition of a stiffer potential at close approaches of the Cu and O-atoms. The DII originates from random phase shifts of vibrating O atoms that have brief ($\ensuremath{\sim}10\phantom{\rule{0.28em}{0ex}}\mathrm{fs}$) anharmonic interactions with neighboring Cu atoms. The spectrum of DII gives information about the interaction time of anharmonic interactions between atoms, and its intensity gives a strength of coupling between vibrating atoms and a thermal bath.