Signatures of the topological s+- superconducting order parameter in the type-II Weyl semimetal Td-MoTe2

In its orthorhombic T-d polymorph, MoTe2 is a type-II Weyl semimetal, where the Weyl fermions emerge at the boundary between electron and hole pockets. Non-saturating magnetoresistance and superconductivity were also observed in T-d-MoTe2. Understanding the superconductivity in T-d-MoTe2, which was proposed to be topologically non-trivial, is of eminent interest. Here, we report high-pressure muon-spin rotation experiments probing the temperature-dependent magnetic penetration depth in T-d-MoTe2. A substantial increase of the superfluid density and a linear scaling with the superconducting critical temperature T-c is observed under pressure. Moreover, the superconducting order parameter in T-d-MoTe2 is determined to have 2-gap s-wave symmetry. We also exclude time-reversal symmetry breaking in the superconducting state with zero-field mu SR experiments. Considering the strong suppression of T-c in MoTe2 by disorder, we suggest that topologically non-trivial s(+-) state is more likely to be realized in MoTe2 than the topologically trivial s(++) state.