Multigap superconductivity in sesquicarbides La2C3 and Y2C3

A complex structure of the superconducting order parameter in Ln(2)C(3) (Ln=La,Y) is demonstrated by muon spin relaxation measurements in their mixed state. The muon depolarization rate [sigma(nu)(T)] exhibits a characteristic temperature dependence that can be perfectly described by a phenomenological double-gap model for nodeless superconductivity. While the magnitude of two gaps is similar between La2C3 and Y2C3, a significant difference in the interband coupling between those two cases is clearly observed in the behavior of sigma(nu)(T).