Muon-spin-rotation study of the superconducting properties of Mo ₃Sb₇

We present the microscopic properties of superconducting state in Mo3 Sb7 (Tc =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 λ, coherence length ξ, superconducting carrier density ns, and effective-mass enhancement m* have been found to be λ≈665 nm, ξ ≈ 12.5 nm, ns ≈ 1.2× 1027 carriers/ m3, and m* ≈ 18.7 me, respectively.