Topological phases in pyrochlore thallium niobate Tl2Nb2O6-x
Topological phases in pyrochlore thallium niobate Tl2Nb2O6-x
复制标题
烧绿石铌酸铊 Tl2Nb2O6-x 中的拓扑相
DOI：
10.1038/s41524-019-0245-5
复制
发表时间：
2019
影响因子：
9.7
通讯作者：
Weng Hongming
中科院分区：
文献类型：
--
作者：
Zhang Wei;Luo Kaifa;Chen Zhendong;Zhu Ziming;Yu Rui;Fang Chen;Weng Hongming
新型拓扑电子材料的发现为揭示新物理学提供了契机。到目前为止，许多材料已被理论上提出和实验证明托管不同种类的拓扑状态。不幸的是，几乎没有令人信服的实验证据证明拓扑氧化物的存在。原因是氧的氧化通常导致离子晶体，并且使得带反转不太可能。此外，在单一材料中实现不同的拓扑状态是相当困难的，但强烈需要探索拓扑相变。利用第一性原理计算和对称性分析，我们提出氧在烧绿石Tl_2Nb_2O_6 +x（0 ≤x≤ 1.0）中的连续固溶体可以产生多种拓扑态.拓扑绝缘体、狄拉克半金属和三重简并节点半金属可以通过改变氧含量和/或调节晶体对称性来实现。当x = 1时，它是一种二次带接触点在费米能级的半金属。它转变为狄拉克半金属或拓扑绝缘体取决于面内应变。当x = 0.5时，Tl_2Nb_2O_（6.5）中的反转对称性自发破缺，产生三重简并结点。当x = 0时，Tl_2Nb_2O_6变成了一个普通的绝缘体，带隙很窄。由于Tl+和Tl 3+价态的变化，这些由氧固溶体驱动的拓扑相变是唯一的，物理上是合理的。这种拓扑氧化物在关联诱导拓扑态的研究和应用方面有着广阔的前景。
The discovery of new topological electronic materials brings a chance to uncover new physics. Up to now, many materials have been theoretically proposed and experimentally proved to host different kinds of topological states. Unfortunately, there is little convincing experimental evidence for the existence of topological oxides. The reason is that oxidation of oxygen leads to ionic crystal in general and makes band inversion unlikely. In addition, the realization of different topological states in a single material is quite difficult, but strongly needed for exploring topological phase transitions. In this work, using first-principles calculations and symmetry analysis, we propose that the experimentally tunable continuous solid solution of oxygen in pyrochlore Tl2Nb2O6+x(0 ≤x≤ 1.0) leads to various topological states. Topological insulator, Dirac semimetal, and triply degenerate nodal point semimetal can be realized in it via changing the oxygen content and/or tuning the crystalline symmetries. Whenx= 1, it is a semimetal with quadratic band touching point at Fermi level. It transits into a Dirac semimetal or a topological insulator depending on the in-plane strain. Whenx= 0.5, the inversion symmetry is spontaneously broken in Tl2Nb2O6.5, leading to triply degenerate nodal points. Whenx= 0, Tl2Nb2O6becomes a trivial insulator with a narrow band gap. These topological phase transitions driven by solid solution of oxygen are unique and physically plausible due to the variation of valence state of Tl+and Tl3+. This topological oxide will be promising for studying correlation induced topological states and potential applications.