Anomalous superconducting-gap symmetry of noncentrosymmetric La2 C3 observed by ultrahigh-resolution photoemission spectroscopy

We have performed ultrahigh-resolution photoemission spectroscopy on noncentrosymmetric superconductor La2 C3 to study the electronic structure near the Fermi level (EF) and the superconducting-gap symmetry. We clearly observed the opening of the superconducting gap, as evidenced by the emergence of a sharp quasiparticle peak just below EF together with the leading-edge shift toward higher binding energy. Quantitative analysis of the gap function has revealed a marked deviation from the single s - or d -wave symmetry, suggesting the existence of multiple superconducting gaps.