Observation of a BCS Spectral Function in a Conventional Superconductor by Photoelectron Spectroscopy

Abstract

We present high-resolution photoelectron spectra on the $A15$-type conventional superconductor $\mathrm{V}{}_{3}\mathrm{Si}$, where---for the first time---both singularities of the BCS density of states can be resolved by photoemission spectroscopy (PES). With a transition temperature of about ${T}_{c}\ensuremath{\approx}17\mathrm{K}$ the gap ${\ensuremath{\Delta}}_{\mathrm{gap}}$ of this compound has a magnitude of approximately 5 meV. A measurement by PES on this small energy scale requires a very high energy resolution $(\ensuremath{\Delta}E\ensuremath{\lesssim}5\mathrm{meV})$ and sample temperatures significantly below ${T}_{c}$.