Relation between Superconducting Gap Minima and Nesting Vector in YNi2B2C

TL;DR

This study uses high-resolution photoemission spectroscopy to reveal complex superconducting gap anisotropy in YNi2B2C, linking gap minima to Fermi surface nesting vectors and highlighting the intricate nature of superconductivity in borocarbides.

Contribution

It provides the first direct observation of detailed superconducting gap anisotropy and its relation to Fermi surface nesting in YNi2B2C.

Findings

Large superconducting gap anisotropy observed.

Point-like gap minimum connected to nesting vector.

Superconducting gap varies smoothly along some FS intersections.

Abstract

We have performed ultrahigh-resolution angle-resolved photoemission spectroscopy to directly observe the large superconducting (SC) gap anisotropy (GA) of YNi2B2C. The result shows large SC GA with a smooth variation along an intersection of a Fermi surface (FS) around the $\Gamma$-Z line and nearly isotropic SC gap values for two intersections of FSs around the X-P line but with a point-like non-zero minimum only for one sheet. The point-like SC gap minimum can be connected by the nesting vector reported from band calculations. The results show unexpectedly complicated SC GA of borocarbide superconductors.