Straintronic Effect on Phonon-Mediated Superconductivity of Nb₂CT₂ (T = O, S, Se, or Te) MXenes

The electronic structures, phonon dispersions, and electron–phonon coupling of Nb 2 CT 2 (T = O, S, Se, or Te) MXenes were investigated via first-principles calculations. Different models of Nb 2 CT 2 were constructed, and the results show that the low-energy models of Nb 2 CT 2 are intrinsic phonon-mediated superconductors. Of the four Nb 2 CT 2 MXenes, Nb 2 CO 2 MXene exhibits the largest superconducting critical temperature ( T c ) of 14.43 K. The existence of soft modes induced by Kohn anomalies and the contribution of Nb atoms to the Fermi level lead to strong electron–phonon coupling (λ = 0.92) in Nb 2 CO 2 MXene. The T c of Nb 2 CO 2 is further enhanced by biaxial tensile strain and reaches up to 18.28 K under 4% tensile strain. The predicted T c of Nb 2 CS 2 is 4.5 K, which is comparable with experimental data. These findings will further stimulate the search for superconducting MXenes.