Signatures of the topological s +− superconducting order parameter in the type-II Weyl semimetal T d -MoTe 2

In its orthorhombic T d polymorph, MoTe 2 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 -MoTe 2 . Understanding the superconductivity in T d -MoTe 2 , 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 -MoTe 2 . 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 -MoTe 2 is determined to have 2-gap s -wave symmetry. We also exclude time-reversal symmetry breaking in the superconducting state with zero-field μSR experiments. Considering the strong suppression of T c in MoTe 2 by disorder, we suggest that topologically non-trivial s +− state is more likely to be realized in MoTe 2 than the topologically trivial s ++ state.