Temperature-dependent phonon lifetimes in lead investigated with neutron-resonance spin-echo spectroscopy

An experimental study of phonon lifetimes in lead using a novel high-resolution neutron spectrometer is presented. The spectrometer combines the neutron-resonance spin-echo and the three-axis techniques. Transverse-acoustic phonon modes in the low-q limit along the high-symmetry directions are investigated at temperatures between 5-300 K. We apply an analytical approach based on a Gaussian approximation of the instrumental resolution function to separate intrinsic lifetimes from artifactual damping due to sample mosaicity and curvature of the four-dimensional dispersion surface. Observed linewidths are significantly lower than predicted by a theoretical model of anharmonic lattice dynamics based on a force-constant parametrization of the interatomic potential. In the high-symmetry directions the q dependence of the linewidth is found to be linear. No change in lifetime is observed at the superconducting transition temperature T-C