Two-Dimensional Molybdenenes: Superconductivity and Strain-Induced Charge Density Wave.

Abstract

Molybdenene was recently synthesized, yet its theoretically proposed structure shows dynamic instability, making its ground-state structure elusive. Here, we resolve this via first-principles calculations combining structural search, phonon analysis, and electron-phonon coupling. We identify a stable monoclinic α phase and a metastable β phase, both energetically lower than the previously reported stable buckled hexagonal γ phase. The soft mechanical character explains the dynamically unstable structures observed in experiments. All three molybdenenes (α, β, and γ) are metallic and exhibit phonon-mediated superconductivity with Tc ∼ 5 K. For the α phase, biaxial strain of -2% boosts Tc to 9.05 K, while 12% tensile strain induces a 2 × 2 charge density wave (CDW) order. Topological analysis further identifies α and γ phases as topological metals. Our findings establish molybdenene as a pristine 2D elemental platform integrating superconductivity, tunable CDW, and topology.