Bulk superconducting gap of V₃Si studied by low-energy ultrahigh-resolution photoemission spectroscopy

We have performed low-energy ultrahigh-resolution photoemission spectroscopy (PES) of A15 compound V₃Si with a xenon-plasma discharge lamp to elucidate the bulk superconducting gap. Below the superconducting transition temperature (T_c = 15.9 K), we found a sharp quasiparticle peak at the Fermi level in the PES spectrum. The gap spectrum is well fitted by a single s-wave superconducting-gap function together with a dip structure at ∼30 meV suggestive of a strong electron-phonon coupling. The anomalous in-gap state previously observed in the PES measurement with high-energy photons is absent or negligibly small in the present bulk-sensitive measurement. The present PES result shows that V₃Si is a single-gap s-wave superconductor.