Hydrogen functionalization and strain tuning of superconductivity and charge density waves in MXene-derived chalcogenide monolayers

Abstract

Two-dimensional MXene-derived chalcogenides offer a versatile platform for tailoring quantum states. Using first-principles calculations, we investigate the M₂S (M = 3d, 4d) monolayers and their hydrogen-functionalized derivatives to enhance superconductivity and explore competing charge density waves (CDW). Pristine phases exhibit modest superconducting transition temperatures (T_c), but full hydrogenation induces three distinct adsorption geometries (α, β, γ), significantly boosting T_c. Within the McMillan–Allen–Dynes framework, β-Ru₂SH₂ and β-Tc₂SH₂ show promise, while fully anisotropic Migdal–Eliashberg calculations predict T_c values of 20–47.75 K, reaching 51 K in γ-Ru₂SH₂ under 1% compressive strain. Notably, γ-Tc₂SH₂ and α-Ru₂SH₂ exhibit CDW instabilities driven by strong electron–phonon coupling, distinct from conventional Fermi surface nesting. These findings highlight hydrogen functionalization and strain as powerful strategies for designing high-T_c superconductors with coexisting quantum orders in MXene-derived systems. While T_c values depend on computational approximations, the robust trends and interplay of CDW and superconductivity offer actionable insights for experimental synthesis and exploration of novel quantum materials.