Hung Sheng-Hsiung, Jeng Horng-Tay
Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan.
Physics Division, National Center for Theoretical Sciences, Hsinchu 30013, Taiwan.
Materials (Basel). 2020 Oct 1;13(19):4381. doi: 10.3390/ma13194381.
The rare-earth hexaboride SmB, known as the topological Kondo insulator, has attracted tremendous attention in recent years. It was revealed that the topological phase of SmB is insensitive to the value of on-site Coulomb interactions (Hubbard U), indicating that the topological phase in SmB is robust against strong correlations. On the contrary, the isostructural YbB displays a sensitivity to the Hubbard U value. As U increases, YbB transforms from topological Kondo insulator to trivial insulator, showing the weak robustness of the topological phase of YbB against U. Consequently, the dependence of the topological phase on Hubbard U is a crucial issue in the rare-earth hexaboride family. In this work, we investigate the structural and electronic properties of rare-earth hexaboride compounds through first-principles calculations based on density functional theory. By taking the strong correlations into consideration using a wide range of on-site U values, we study the evolution of the topological phases in rare-earth hexaboride (XB, X = La, Ce, Pr, Nd, Pm, Sm, Eu). Unlike YbB, the topological trends in all the examples of XB studied in this work are insensitive to the U values. We conclude that in addition to the well-known SmB, PmB, NdB and EuB are also topologically nontrivial compounds, whereas LaB, CeB and PrB are topologically trivial metal.
稀土六硼化物SmB，即拓扑近藤绝缘体，近年来引起了极大关注。研究表明，SmB的拓扑相对于在位库仑相互作用（哈伯德U）的值不敏感，这表明SmB中的拓扑相对于强关联具有鲁棒性。相反，同结构的YbB对哈伯德U值敏感。随着U的增加，YbB从拓扑近藤绝缘体转变为平凡绝缘体，这表明YbB的拓扑相对U的鲁棒性较弱。因此，拓扑相对哈伯德U的依赖性是稀土六硼化物家族中的一个关键问题。在这项工作中，我们通过基于密度泛函理论的第一性原理计算来研究稀土六硼化物化合物的结构和电子性质。通过使用广泛的在位U值来考虑强关联，我们研究了稀土六硼化物（XB，X = La、Ce、Pr、Nd、Pm、Sm、Eu）中拓扑相的演变。与YbB不同，本工作中研究的所有XB例子中的拓扑趋势对U值不敏感。我们得出结论，除了众所周知的SmB之外，PmB、NdB和EuB也是拓扑非平凡化合物，而LaB、CeB和PrB是拓扑平凡金属。
