Comment on ``Muon-spin rotation studies of the superconducting properties of Mo3Sb7'', Phys.Rev.B 78, 172505 (2008)
Abstract
In a recent article Tran et al. [Phys. Rev.B 78, 172505 (2008)] report on the result of the muon-spin rotation (μSR) measurements of Mo3Sb7 superconductor. Based on the analysis of the temperature and the magnetic field dependence of the Gaussian relaxation rate σsc they suggest that Mo3Sb7 is the superconductor with two isotropic s-wave like gaps. An additional confirmation was obtained from the specific heat data published earlier by partly the same group of authors in [Acta Mater. 56, 5694 (2008)]. The purpose of this Comment is to point out that from the analysis made by Tran et al. the presence of two superconducting energy gaps in Mo3Sb7 can not be justified. The analysis of μSR data does not account for the reduction of σsc with increasing temperature, and, hence, yields inaccurate information on the magnetic penetration depth. The specific heat data can be satisfactory described within the framework of the one-gap model with the small residual specific heat component. The experimental data of Tran et al., as well as our earlier published μSR data [Phys. Rev. B 78, 014502 (2008)] all seem to be consistent with is the presence of single isotropic superconducting energy gap in Mo3Sb7.