Surface superconductivity in the Weyl semimetal MoTe2 detected by point contact spectroscopy

Abstract

MoTe2 is a Weyl semimetal, which exhibits unique non-saturating magnetoresistance and strongly reinforced superconductivity under pressure. Here, we demonstrate that a novel mesoscopic superconductivity at ambient pressure arises on the surface of MoTe2 with a critical temperature up to 5 K significantly exceeding the bulk Tc = 0.1 K. We measured the derivatives of I-V curves for hetero-contacts of MoTe2 with Ag or Cu, homo-contacts of MoTe2 as well as 'soft' point contacts (PCs). Large number of these hetero-contacts exhibit a dV/dI dependence, which is characteristic for Andreev reflection. It allows us to determine the superconducting gap Δ. The average gap values are 2Δ = 1.30 ± 0.15 meV with a 2Δ/kBTc ratio of 3.7 ± 0.4, which slightly exceeds the standard BCS value of 3.52. Furthermore, the temperature dependence of the gap follows a BCS-like behavior, which points to a nodeless superconducting order parameter with some strong-coupling renormalization. Remarkably, the observation of a 'gapless-like' single minimum in the dV/dI of 'soft' PCs may indicate a topological superconducting state of the MoTe2 surface as these contacts probe mainly the interface and avoid additional pressure effect. Therefore, MoTe2 might be a suitable material to study new forms of topological superconductivity.