Muon-spin-rotation study of the superconducting properties of Mo3Sb7

We present the microscopic properties of superconducting state in Mo(3)Sb(7) (T(c)=2.2 K) using muon-spin rotation measurements. The zero-field-cooled and field-cooled (FC) data with an applied transverse field of 40 mT reveal an irreversibility in the muon relaxation rates and precessional frequencies below 2 K. We have also found an anomaly around 0.5 K, which may be related to a process of the vortex melting or some change in vortex-lattice symmetry. The temperature dependence of FC muon relaxation rate can be analyzed using a phenomenological double-gap s-wave model. The observation of a nonlinear field dependence of the muon relaxation rate is consistent with the occurrence of two superconducting gaps. Moreover, the magnetic penetration depth lambda, coherence length xi, superconducting carrier density n(s), and effective-mass enhancement m(*) have been found to be lambda approximate to 665 nm, xi approximate to 12.5 nm, n(s)approximate to 1.2x10(27) carriers/m(3), and m(*)approximate to 18.7m(e), respectively.