Fermi-Surface-Sheet Dependent Electron-Phonon Coupling in a Borocarbide Superconductor YNi_{2}B_{2}C.

We performed de Haas-van Alphen (dHvA) oscillation measurements and band-structure calculations for YNi_{2}B_{2}C. Our improved band structure successfully explained the origins of the large dHvA frequencies β and ζ, which were inexplicable in previous works. By comparing experimental effective masses with band masses, we determined the electron-phonon coupling for each orbit. The results showed a clear Fermi-surface-sheet dependence of the electron-phonon coupling strength, especially highlighting that the coupling for the band-28 sheet is very weak, almost absent for the orbit with B∥c. This finding is consistent with previous observations of dHvA oscillations from this orbit in the mixed state down to very low fields. Amid growing interest in high-temperature superconductivity driven by electron-phonon coupling in hydrides under high pressure, this Letter provides foundational data pivotal to precisely understanding electron-phonon coupling.