Topological Phase and Strong Correlation in Rare-Earth Hexaborides XB(6) (X = La, Ce, Pr, Nd, Pm, Sm, Eu)

The rare-earth hexaboride SmB(6), known as the topological Kondo insulator, has attracted tremendous attention in recent years. It was revealed that the topological phase of SmB(6) is insensitive to the value of on-site Coulomb interactions (Hubbard U), indicating that the topological phase in SmB(6) is robust against strong correlations. On the contrary, the isostructural YbB(6) displays a sensitivity to the Hubbard U value. As U increases, YbB(6) transforms from topological Kondo insulator to trivial insulator, showing the weak robustness of the topological phase of YbB(6) 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(6), X = La, Ce, Pr, Nd, Pm, Sm, Eu). Unlike YbB(6), the topological trends in all the examples of XB(6) studied in this work are insensitive to the U values. We conclude that in addition to the well-known SmB(6), PmB(6), NdB(6) and EuB(6) are also topologically nontrivial compounds, whereas LaB(6), CeB(6) and PrB(6) are topologically trivial metal.