Designing flexible quantum spin hall insulators through 2D ordered hybrid transition-metal carbides

Abstract

Quantum spin Hall (QSH) insulators have attracted much attention due to their potential applications ranging from electronic devices to quantum computing. In general, a large band gap is regarded as a critical descriptor in the design of QSH insulators; however, it faces challenges when additional factors such as strain and surface oxidation are involved in practical applications. In this work, taking M '' M-2'C2O2 (M' = Ti, Zr, Hf; M '' = Mo, W) as a representative, results reveal that 2D ordered transition-metal carbides (MXenes) are promising candidates for flexible spintronic devices, which is ascribed to the mechanical flexibility and robust QSH states under strain. Although a large bulk band gap is shown in M '' 2HfC2O2, a strain-induced topological phase transition may limit its flexible application. On the contrary, M '' 2TiC2O2 has a smaller,gap, and its topological nontrivial state survives under strain. When n changes from 0 to 4 in M '' 2TinCn+1O2, a topologically nontrivial-trivial phase transition is observed in W2HfnCn+1O2, whereas a topologically nontrivial state remains in Mo2TinCn+1O2. After further screening a variety of promising coatings, it is found that fluorographene may effectively preserve the topologically nontrivial nature of M '' M-2'C2O2 with surface oxidation resistance, even under strain, providing a feasible application of M '' M-2'C2O2 as flexible QSH insulators.