Observation of a BCS spectral function in a conventional superconductor byphotoelectron spectroscopy

We present high-resolution photoelectron spectra on the A15-type convention al 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 Delt a (gap) of this compound has a magnitude of approximately 5 meV. A measurem ent by PES on this small energy scale requires a very high energy resolutio n (DeltaE less than or similar to5 meV) and sample temperatures significant ly below T-c.