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 T-c approximate to 17 K the gap Delta (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 (DeltaE less than or similar to5 meV) and sample temperatures significantly below T-c.