Magnetic-field dependence of superconducting energy gaps in YNi₂B₂C: Evidence of multiband superconductivity

Abstract

We present results of an in-field directional point-contact spectroscopy study of the quaternary borocarbide superconductor YNi₂B₂C, which is characterized by a highly anisotropic superconducting gap function. For I∥a, the superconducting energy gap (Δ), decreases linearly with magnetic field and vanishes at around 3.25T, which is well below the upper critical field (H_c2∼6T) measured at the same temperature (2K). For I∥c, on the other hand, Δ decreases weakly with magnetic field but the broadening parameter (Γ) increases rapidly with magnetic field with the absence of any resolvable feature above 3.5T. From an analysis of the field variation of energy gaps and the zero-bias density of states we show that the unconventional gap function observed in this material could originate from multiband superconductivity.