Enhancement of superconductivity in Zr2S2C arisingfrom phonon softening on transition from bulk tomonolayer

Abstract We report a new compound, Zr 2 S 2 C, belonging to the transition metal carbo-chalcogenide (TMCC) family. Through first-principles calculations, our analysis of phonon dispersion spectra indicates that the compound is dynamically stable in both bulk and monolayer forms. We systematically investigated the electronic structure, phonon dispersion, and electron–phonon coupling (EPC) driven superconducting properties in bulk and monolayer Zr 2 S 2 C. The results demonstrate the metallic character of bulk Zr 2 S 2 C, with a weak EPC strength ( λ ) of 0.41 and superconducting critical temperature ( T c ) of ∼3 K. The monolayer Zr 2 S 2 C has an enhanced λ of 0.62 and T c of ∼6.4 K. The increased λ value in the monolayer results from the softening of the acoustic phonon mode. We found that when biaxial strain is applied, the low energy acoustic phonon mode in monolayer becomes even softer. This softening leads to a transformation of the Zr 2 S 2 C monolayer from its initial weak coupling state ( λ = 0.62) to a strongly coupled state, resulting in an increased λ value of 1.33. Consequently, the superconducting critical temperature experiences a twofold increase. These findings provide a theoretical framework for further exploration of the layered two-dimensional TMCC family, in addition to offering valuable insights.