First‐principles study of f‐orbital‐dependent band topology of topological rare earth hexaborides

Abstract The rare earth hexaboride (RE)B 6 series of compounds (RE = Ce, Pr, Nd, Pm, Sm, Eu, Gd) was investigated using the first‐principles approach for exploring new topological insulators. The calculated structural, electronic, and magnetic properties of the materials are discussed in detail. To account for better f ‐electron correlation, the Hubbard correction was also tested to correct the Kondo states. The lattice appeared contracted for materials from CeB 6 to GdB 6 , and charge is transferred from RE to boron. The inspection of band structure points to spd hybridization between RE‐ 5d and B‐ 2s , 2p states at Fermi level. The application of spin‐orbit coupling revealed the conversion in the parity, and an odd number of Dirac cones is found at Γ and X points without Kondo mechanism. PrB 6 , GdB 6 , and PmB 6 revealed a dispersive conic region near the Fermi level at high symmetry points, which enclosed Kramer's degenerate points with surface states of opposite parity. These materials prove to be a strong topological Kondo insulator with an SmB 6 ‐like cubic structure without involvement of f‐orbitals in the formation of a Dirac cone. The Hubbard U parameter determined from atomic calculation of RE f‐ orbital, apart from the few cases when f ‐states remain close to the Fermi level, revealed that the band structures are semimetallic in most cases.