# Possible topologically non-trivial superconducting order parameter in type-II Weyl semimetal T_d-MoTe_2

## TL;DR

This study investigates the superconducting properties of T_d-MoTe_2 under pressure, revealing a two-gap s+s-wave order parameter and suggesting a topologically non-trivial s^{+-} pairing state, potentially making it the first time reversal invariant topological Weyl superconductor.

## Contribution

The paper provides experimental evidence for a two-gap s+s-wave superconducting order parameter in T_d-MoTe_2 and proposes a topologically non-trivial s^{+-} pairing symmetry, advancing understanding of topological superconductivity.

## Key findings

- Superfluid density increases with pressure.
- Superconducting gap is two-gap s+s-wave symmetric.
- No time reversal symmetry breaking detected.

## Abstract

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 ${\mu}$SR 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.