Multiband Superconductivity in the Chevrel Phases SnMo6S8 and PbMo6S8

Sub-Kelvin scanning tunneling spectroscopy in the Chevrel phases SnMo6S8 and PbMo6S8 reveals two distinct superconducting gaps with Delta(1) = 3 meV, Delta(2) similar to 1.0 meV and Delta(1) = 3.1 meV, Delta(2) similar to 1.4 meV, respectively. The gap distribution is strongly anisotropic, with Delta(2) predominantly seen when scanning across unit-cell steps on the (001) sample surface. The spectra are well fitted by an anisotropic two-band BCS s-wave gap function. Our spectroscopic data are confirmed by electronic heat capacity measurements, which also provide evidence for a twin-gap scenario.