Electron-phonon coupling (EPC), i.e., the scattering of lattice vibrations by electrons and vice versa, is ubiquitous in solids and can lead to emergent ground states such as superconductivity and charge-density wave order. The strength of EPC in emergent superconducting materials is routinely assessed by ab-initio calculations. However, the accuracy of such calculations is difficult to check.
Here, we report on a comprehensive study of the lattice dynamics in the strong-coupling superconductor YNi2B2C. Employing thermal neutron spectroscopy, we report phonon properties over the full dispersion range, E ≤ 160 meV. At many points we could deduce the intrinsic phonon linewidth and compare it to prediction based on density-functional perturbation theory. Overall, we find excellent agreement. Studies including angle-resolved photoemission spectroscopy revealed that the most prominent phonon anomalies can only be explained by considering the dependence of the EPC on both, the electron-momentum k and the phonon-momentum q . We show that strong phonon broadening can occur in the absence of both Fermi surface nesting and lattice anharmonicity, if EPC is strongly enhanced for specific values of electron-momentum, k. This new scenario likely applies to a wide range of compounds.
 Kurzhals, P. et al. Electron-momentum dependence of electron-phonon coupling underlies dramatic phonon renormalization in YNi2B2C. Nat Commun 13, 228, doi:10.1038/s41467-021-27843-y (2022).
Dr. Jitae Park
Dr. Theresia Heiden-Hecht
Dr. Dominic Hayward