Tunable Superconductivity in Functionalized Janus MoSeA (A = H, Li) Monolayers: Competition between Lattice Instability and Electron Pairing

Two-dimensional (2D) materials with tunable charge transport and lattice dynamics provide an attractive platform for energy-efficient electronic and quantum devices. In such systems, superconductivity is often limited by competing lattice instabilities. Identifying control parameters that stabilize the lattice while enhancing electron–phonon coupling is therefore essential for the design of functional superconducting materials. In this work, we investigate tunable superconductivity in functionalized Janus MoSeA (A = H, Li) monolayers using first-principles density functional theory, density functional perturbation theory, and fully anisotropic Migdal–Eliashberg calculations. Janus asymmetry combined with surface functionalization enables systematic control of charge redistribution, lattice stability, and pairing strength. We find that lithium functionalization stabilizes the hexagonal 2H phase of MoSeLi, yielding a metallic monolayer with moderate electron–phonon coupling and multiband superconductivity. In contrast, hydrogen-functionalized 2H–MoSeH exhibits a pronounced lattice instability that suppresses superconductivity by removing the spectral weight at the Fermi level. This instability can be suppressed through external perturbations such as hole doping or biaxial compressive strain, enabling superconductivity with transition temperatures approaching 31 K. These results reveal a clear competition between lattice instability and electron–phonon pairing, in which stabilizing the lattice decisively favors superconductivity. From an applied perspective, the superconducting properties of Janus MoSeA monolayers can be tuned by using experimentally accessible control parameters, including substrate-induced strain, electrostatic gating, and chemical functionalization. Our findings establish a general design principle for tunable superconductivity in two-dimensional energy materials.