Hourglass-type bulk Ni 3d band and Ce 4 f Kondo resonance states in the potential topological Kondo semimetal CeNiSn via angle-resolved photoemission spectroscopy

The electronic structure of CeNiSn, which is a potential topological Kondo insulator and a Dirac nodal -loop semimetal, has been investigated by employing temperature (T ) dependent angle-resolved photoemission spectroscopy (ARPES). The Fermi surfaces (FSs) and the band structures of CeNiSn for three orthogonal crystallographic planes are measured, in which both the very dispersive bands and the flat bands are observed, having mainly the Ni 3d character and the Ce 4 f character, respectively. The measured FSs and ARPES bands agree reasonably well with the density functional theory (DFT) calculations. The Fermi-edge (EF) photon energy (h nu) map along kb (= k(010)) shows that the metallic EF-crossing states on the (010) surface have the three-dimensional character, suggesting that the observed EF-crossing metallic states do not correspond to the topological surface states of the two-dimensional character. On the other hand, albeit weak, the features of the hourglass-type bulk band crossings are observed along SXS, with the energies and the slopes being similar to those predicted by the DFT calculations, supporting the Dirac semimetallic nature of CeNiSn. In T-dependent ARPES, the Ce 4 f Kondo resonance states are clearly revealed at low T, which become much suppressed above -80 K. This feature is consistent with the Kondo temperature of CeNiSn, estimated from its rho(T) data. This work demonstrates the importance of the coherent Kondo states in determining the topological properties of CeNiSn.