Two-band superconductivity with weak interband coupling in structurally disordered Y5Rh6Sn18

Temperature variation of the lower critical field Hc1(T) in the structurally disordered superconductor Y₅Rh₆Sn₁₈ with a transition temperature Tc3.2 K was investigated using micro-Hall-probe magnetometry for local magnetization measurements. Down to about 0.45Tc, an Hc1(T) dependence typical for a single-band s-wave BCS superconductor was observed. However, deep within the superconducting state, a sudden increase of Hc1(T) was found, indicating the presence of a two-band effect. By applying the two-gap γ model to Y₅Rh₆Sn₁₈, we revealed a very weak interband coupling in this skutterudite-related material. We speculate that the two-band superconductivity in Y₅Rh₆Sn₁₈ is a base for the boosted Tc in slightly doped samples, which likely reflects a mechanism for enhancing superconductivity by disorder.