Electronic and topological band evolution of VB-group transitionmetal monocarbides M₂C (M=V, Nb, or Ta) bulk and monolayer

Authors

Ali Sufyan; Aniceto B. Maghirang; Gennevieve M. Macam; Zhi-Quan Huang; Chia-Hsiu Hsu; Feng-Chuan Chuang

Source

Mater. Today Commun. 32, 103875 (2022). DOI: 10.1016/j.mtcomm.2022.103875

Keywords:

Electronic structures, First-principles calculations, Mono-transition metal MXenes, Topological insulators, Topological phase transition, Transition metal monocarbides

Abstract

Two-dimensional transition metal monocarbides (2D MXenes) have attracted intense interest due to their versatility, predicted topological phase, and immense applications. In this study, we investigated the electronic and topological band evolutions of both the bulk and monolayer MXenes, M₂C (M = V, Nb, or Ta), using first-principles calculations. Our study shows that all the three bulk M₂C are semi-metallic and host topological phases. Interestingly, our study showed pristine monolayers V₂C and Nb₂C exhibit non-trivial topological phases, while Ta₂C exhibits trivial phase. Unlike other MXenes, monolayer V₂C and Nb₂C host the quantum spin Hall effect without functionalizations. Furthermore, thickness-dependent calculations intriguingly show Lifshitz electronic transition from semi-metallic to topological insulating phase in V₂C from bilayer to monolayer with a sufficiently large bandgap of 0.32 eV. Moreover, the topological phase transition between the TI state and the trivial state in V₂C is driven by quantum size effects as the Z₂ topological invariant notably oscillates between 1 and 0 with varying thickness. Finally, our study demonstrated that VB MXenes could be promising topological materials for spintronics applications.