Topological properties of CeNiSn, CeRhAs, and CeRhSb: hourglass-type crossing and Dirac nodal-loop bulk band structure

Topological Kondo insulators draw a great deal of recent attention, and so research on conventional Kondo insulators is actively revived. SmB6 is a typcial example. Among Ce-based systems, CeNiSn, CeRhSb, and CeRhAs were recently predicted to have exotic topological surface states that has been intensively studied by electrical resistivity and optical conductivity measurement. To investigate whether these materials are promising candidate of topological Kondo insulators, we have investigated the electronic structures of CeNiSn, CeRhSb, and CeRhAs, employing the density functional theory and the dynamical mean field theory (DMFT). For all three systems, we have obtained the hourglass-type bulk band crossings around k=S, which produce a Dirac nodal-loop centered at S in the [100] BZ boundary. This nodal-loop band crossing is guaranteed by crystal symmetry. In addition, from the DMFT calculations, we have found that the hourglass-type band structure along X-S line penetrates through the Ce f-level near the Fermi energy, resulting from the hybridization effect between the different characters of bands. This gives the possible change of topological property upon T variation. This work introduces new type of nodal-loop Dirac semimetal, especially when f level is involved in the system.