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

Here, the electronic structures, phonon dispersions, and electron–phonon coupling of Nb₂CT₂ (T = O, S, Se, or Te) MXenes were investigated via first-principles calculations. Different models of Nb₂CT₂ were constructed, and the results show that the low-energy models of Nb₂CT₂ are intrinsic phonon-mediated superconductors. Of the four Nb₂CT₂ MXenes, Nb₂CO₂ 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 Nb₂CO₂ MXene. The $T_c$ of Nb₂CO₂ is further enhanced by biaxial tensile strain and reaches up to 18.28 K under 4% tensile strain. The predicted $T_c$ of Nb₂CS₂ is 4.5 K, which is comparable with experimental data. These findings will further stimulate the search for superconducting MXenes.