Fermi-surface-sheet dependent electron-phonon coupling in a borocarbide superconductor YNi$_2$B$_2$C

TL;DR

This study investigates how electron-phonon coupling varies across different Fermi surface sheets in YNi$_2$B$_2$C, revealing a sheet-dependent coupling strength crucial for understanding superconductivity in this material.

Contribution

It provides detailed experimental and theoretical analysis of Fermi-surface-dependent electron-phonon coupling in YNi$_2$B$_2$C, highlighting the weak coupling on a specific Fermi surface sheet.

Findings

Electron-phonon coupling varies across Fermi surface sheets.

Coupling is very weak or absent on the band-28 sheet.

Results support previous observations of dHvA oscillations in the mixed state.

Abstract

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 $\beta$ and $\zeta$, 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 $B \parallel c$. This finding is consistent with previous observations of dHvA oscillations from this orbit in the mixed state down to very low fields. Amidst growing interest in high-temperature superconductivity driven by electron-phonon coupling in hydrides under high pressure, this study provides foundational data pivotal to precisely understanding electron-phonon coupling.