npj:非对称材料KHgX—非常规拓扑相变
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来自中国台湾两所大学的Tay-Rong Chang和Horng-Tay Jeng等提出了由Dirac无间隙态介导的两个拓扑非平凡绝缘态之间的非常规拓扑相变体系,该体系源于非对称型晶体对称性,不同于传统的拓扑相变。KHgX(X = As,Sb,Bi)族是第一个实验上实现的拓扑非同态晶体绝缘体,其中拓扑表面态以莫比乌斯扭曲连接为特征。他们基于第一原理计算,通过引入两个新相来使KHgX的拓扑相图多样化。通过施加应力,KHgX经历拓扑绝缘体-金属的转变,从拓扑非同态晶体绝缘体相转变为Cm = -2的DSM相,在非对称晶体结构中的非平凡镜Chern数Cm = -3。通过对称性破坏,DSM相转换为另一个新的拓扑非同态晶体绝缘体相,其中Cm = -3主导着QSH效应。表面能带的连通性的变化,提供了拓扑相变的直接证明,而且要实现这些预测的新拓扑相,操纵带隙是其关键。
该文近期发表于npj Computational Materials 5: 65 (2019),英文标题与摘要如下,点击左下角“阅读原文”可以自由获取论文PDF。
Unconventional topological phase transition in non-symmorphic material KHgX (X = As, Sb, Bi)
Chin-Shen Kuo, Tay-Rong Chang, Su-Yang Xu & Horng-Tay Jeng
Traditionally topological phase transition describes an evolution from topological trivial to topological nontrivial state. Originated from the non-symmorphic crystalline symmetry, we propose in this work an unconventional topological phase transition scheme between two topological nontrivial insulating states mediated by a Dirac gapless state, differing from the traditional topological phase transition. The KHgX (X = As, Sb, Bi) family is the first experimentally realized topological non-symmorphic crystalline insulator (TNCI), where the topological surface states are characterized by the Mobius-twisted connectivity. Based on first-principles calculations, we present a topological insulator–metal transition from TNCI into a Dirac semimetal (DSM) via applying an external pressure on KHgX. We find an unusual mirror Chern number Cm = −3 for the DSM phase of KHgX in the non-symmorphic crystal structure, which is topologically distinct from the traditional DSM such as Na3Bi and Cd3As2. Furthermore, we predict a new TNCI phase in KHgX via symmetry breaking. The topological surface states in this new TNCI phase display zigzag connectivity, different from the unstressed one. Our results offer a comprehensive study for understanding how the topological surface states evolve from a quantum.
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