Phase evolution and superconductivity enhancement in Se-substituted MoTe${}_2$ thin films

Abstract

The strong spin$-$orbit coupling (SOC) and numerous crystal phases in few$-$layer transition metal dichalcogenides (TMDCs) MX${}_2$ (M$=$W, Mo, and X$=$Te, Se, S) has led to a variety of novel physics, such as Ising superconductivity and quantum spin Hall effect realized in monolayer 2H$-$ and Td$-$MX${}_2$, respectively. Consecutive tailoring of the MX${}_2$ structure from 2H to Td phase may realize the long$-$sought topological superconductivity in one material system by incorporating superconductivity and quantum spin Hall effect together. In this work, by combing Raman spectrum, X-ray photoelectron spectrum (XPS), scanning transmission electron microscopy imaging (STEM) as well as electrical transport measurements, we demonstrate that a consecutively structural phase transitions from Td to 1T${}^{\prime }$ to 2H polytype can be realized as the Se-substitution concentration increases. More importantly, the Se$-$substitution has been found to notably enhance the superconductivity of the MoTe${}_2$ thin film, which is interpreted as the introduction of the two$-$band superconductivity. The chemical constituent induced phase transition offers a new strategy to study the s${}_{+-}$ superconductivity and the possible topological superconductivity as well as to develop phase$-$sensitive devices based on MX${}_2$ materials.

27 pages, 5 figures