One or two gaps in Mo 8 Ga 41 superconductor? Local Hall-probe magnetometry study

The magnetization properties of the endohedral cluster superconductor Mo 8 Ga 41 are studied by sensitive Hall-probe magnetometry. The temperature dependence of the lower critical magnetic field H c 1 is obtained and compared to theoretical models accounting for single-gap and two-gap superconductivity. Data can be described by both models with minor differences. These results are confronted with our previous measurements which evidence that the system is inherently single-gap s -wave superconductor but minor additional phases are present also in seemingly perfect samples. We discuss how presence of such additional phases with varying size of the penetration depth and H c 1 field is reflected in magnetization measurements which could lead to misinterpretation of the multigap superconductivity in Mo 8 Ga 41 .