Superconductivity gap symmetry in monoclinic MoTe2 under pressure

MoTe2, with the orthorhombic Td structure, is a new type (type-II) of Weyl semimetal. Unusual magnetoresistance and superconductivity were also observed in Td MoTe2. Understanding the superconductivity in Td-MoTe2, which was proposed to be topologically nontrivial, is of great interest. We performed high-pressure (pmax = 1.3 GPa) muon spin rotation experiments on the temperature-dependent magnetic penetration depth λ (T) in Td-MoTe2. A substantial increase of the critical temperature Tc and superfluid density ns (0) ~ 1/ λ2(0) is observed under pressure. The temperature dependence of 1/ λ2(T) is inconsistent with the presence of nodes in the gap as well as with a simple isotropic s-wave type of the order parameter. However, it is well described by a 2-gap s-wave model, indicating multigap superconductivity. Observed linear correlation between Tc and the zero-temperature superfluid density ns (0) together with the two-gap behaviour points to the unconventional nature of superconductivity in Td-MoTe2.