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 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 (Tc) 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 Tc of Nb2CO2 is further enhanced by biaxial tensile strain and reaches up to 18.28 K under 4% tensile strain. The predicted Tc of Nb2CS2 is 4.5 K, which is comparable with experimental data. These findings will further stimulate the search for superconducting MXenes.