Andreev Reflection Study of the Superconductor $Mo_3Sb_7$

The point-contact Andreev-reflection measurements on the new paramagnetic superconductor $Mo_3Sb_7$ were carried out. It was found that the order parameter ∆ is strongly anisotropic varying over a very wide range depending on the contact orientation when the maximum $∆_\text{max}$ exceeds at least 40 times the minimum $∆_\text{min}$ in spite of the invariable $T_c$ that cannot be typical of conventional superconductors. For these and other reasons we suggest that $Mo_3Sb_7$ is not a trivial BCS (s-wave) superconductor but rather has some unconventional pairing symmetry.