MoTe_2, with the orthorhombic T_d phase, is a new type (type-II) of Weyl semimetal, where the Weyl Fermions emerge at the boundary between electron and hole pockets. Non-saturating magnetoresistance (MR), 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 (p_max = 1.3 GPa) muon spin rotation experiments on the temperature-dependent magnetic penetration depth in T_d-MoTe_2. A substantial increase of the superfluid density n_s/m^* and a linear scaling with T_c is observed under pressure. Moreover, the superconducting order parameter in T_d-MoTe_2 is determined to be two gap (s+s)-wave symmetric. We also excluded time reversal symmetry breaking in the SC state with sensitive zero-field μSR experiments. Considering the previous report \cite{Balicas1} on the strong suppression of T_c in T_d-MoTe_2 by disorder, we suggest that s^{+-} (topological order parameter) state is more likely to be realized in MoTe_2 than the s^{++} (trivial) state. Should s^{+-} be the SC gap symmetry, the T_d-MoTe_2 is, to our knowledge, the first known example of a time reversal invariant topological (Weyl) superconductor.
@article{arxiv.1704.05185,
title = {Possible topologically non-trivial superconducting order parameter in type-II Weyl semimetal T_d-MoTe_2},
author = {Z. Guguchia and F. v. Rohr and Z. Shermadini and A. T. Lee and S. Banerjee and A. R. Wieteska and C. A. Marianetti and H. Luetkens and Z. Gong and B. A. Frandsen and S. C. Cheung and C. Baines and A. Shengelaya and A. N. Pasupathy and E. Morenzoni and S. J. L. Billinge and A. Amato and R. J. Cava and R. Khasanov and Y. J. Uemura},
journal= {arXiv preprint arXiv:1704.05185},
year = {2018}
}