Electron-phonon coupling in the conventional superconductor YNi ₂B ₂C at high phonon energies studied by time-of-flight neutron spectroscopy

We report an inelastic neutron scattering investigation of phonons with energies up to 159meV in the conventional superconductor YNi ₂B ₂C. Using the sweep mode, a newly developed time-of-flight technique involving the continuous rotation of a single crystal specimen, allowed us to measure a four-dimensional volume in (Q, E) space and, thus, determine the dispersion surface and linewidths of the A _1g (102meV) and A _u (159meV) type phonon modes over the whole Brillouin zone. Despite of having linewidths of Γ=10meV, A _1g modes do not strongly contribute to the total electron-phonon coupling constant λ. However, experimental linewidths show a remarkable agreement with abinitio calculations over the complete phonon energy range, demonstrating the accuracy of such calculations in a rare comparison to a comprehensive experimental data set.