Topological Phase and Strong Correlation in Rare-Earth Hexaborides XB6 (X = La, Ce, Pr, Nd, Pm, Sm, Eu)

Abstract

The rare-earth hexaboride SmB6, known as the topological Kondo insulator, has attracted tremendous attention in recent years. It was revealed that the topological phase of SmB6 is insensitive to the value of on-site Coulomb interactions (Hubbard U), indicating that the topological phase in SmB6 is robust against strong correlations. On the contrary, the isostructural YbB6 displays a sensitivity to the Hubbard U value. As U increases, YbB6 transforms from topological Kondo insulator to trivial insulator, showing the weak robustness of the topological phase of YbB6 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 (XB6, X = La, Ce, Pr, Nd, Pm, Sm, Eu). Unlike YbB6, the topological trends in all the examples of XB6 studied in this work are insensitive to the U values. We conclude that in addition to the well-known SmB6, PmB6, NdB6 and EuB6 are also topologically nontrivial compounds, whereas LaB6, CeB6 and PrB6 are topologically trivial metal.