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

We present high-resolution photoelectron spectra on the $A15$-type conventional superconductor V₃Si, 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 Tc≈17K the gap Δgap 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 (ΔE5meV) and sample temperatures significantly below Tc.