Electronic and topological band evolution of VB-group transitionmetal monocarbides M2C (M=V, Nb, or Ta) bulk and monolayer. (August 2022)

• Record Type: Journal Article
• Authors: Sufyan, Ali; Maghirang, Aniceto B.; Macam, Gennevieve; Huang, Zhi-Quan; Hsu, Chia-Hsiu; Chuang, Feng-Chuan
• Is Part Of: Materials today communications. Volume 32(2022)
• Publication Date: 2022-08
• Subjects: Topological insulators -- Topological phase transition -- Mono-transition metal MXenes -- Transition metal monocarbides -- Electronic structures -- First-principles calculations; Materials science -- Periodicals; 620.11
• DOI: 10.1016/j.mtcomm.2022.103875
• Languages: English
• ISSNs: 2352-4928

Abstract

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, M2 C (M = V, Nb, or Ta), using first-principles calculations. Our study shows that all the three bulk M2 C are semi-metallic and host topological phases. Interestingly, our study showed pristine monolayers V2 C and Nb2 C exhibit non-trivial topological phases, while Ta2 C exhibits trivial phase. Unlike other MXenes, monolayer V2 C and Nb2 C 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 V2 C 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 V2 C 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. Graphical Abstract: ga1 Highlights: The bulk M2 C (M=V, Nb, or Ta) are found to be weak topological insulators (0; 1, 1, 1) with semi-metallic characteristics. A Lifshitz electronic transition from semi-metallic bilayer to the monolayer semiconductor has been observed in V2 C with a large bandgap of 0.32 eV. The pristine monolayer V2 C and Nb2 C are found to be topologically non-trivial while pristine monolayer Ta2 C is a trivial semimetal. Topological phase transition between topologically non-trivial and trivial states occurred in these compounds by varying the thickness.