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Designing Flexible Quantum Spin Hall Insulators through 2D Ordered Hybrid Transition-Metal Carbides

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journal contribution
posted on 07.08.2019, 15:47 by Zhongheng Fu, Zhaorui Liu, Dominik Legut, Timothy C. Germann, Chen Si, Shiyu Du, Joseph S. Francisco, Ruifeng Zhang
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″2M′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″2M′C2O2 with surface oxidation resistance, even under strain, providing a feasible application of M″2M′C2O2 as flexible QSH insulators.