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Phys. Rev. Lett. 114, 016403 (2015)

We present high-resolution angle-resolved photoemission spectroscopy studies of trivalent CeB6 and divalent BaB6 rare-earth hexaborides. We find that the Fermi surface electronic structure of CeB6 consists of large oval-shape pockets around the X points of the Brillouin zone, while the states around the zone centre G point are strongly renormalized. Our first-principles calculations agree with data around the X points, but not at the G points, indicating areas of strong renormalization located around G. The Ce quasi-particle states participate in formation of hotspots at the Fermi surface, while the incoherent f-states hybridize and lead to the emergence of dispersive features absent in non-f counterpart BaB6. These experimental and theoretical results provide a new understanding of rare-earth hexaboride materials.

Fermi surface topology and hotspots distribution in Kondo lattice system CeB6.
Published in Madhab Neupane, N. Alidoust, G. Bian, et al., arXiv:1411:0302 (2014).

We present angle-resolved photoemission studies on the rare-earth- hexaboride YbB6, which has recently been predicted to be a topological Kondo insulator. Our data do not agree with the prediction and instead show that YbB6 exhibits a novel topological insulator state in the absence of a Kondo mechanism. We find that the Fermi level electronic structure of YbB6 has three 2D Dirac cone surface states enclosing the Kramers' points, while the f-orbital that would be relevant for the Kondo mechanism is 1 eV below the Fermi level. Our first-principles calculation shows that the topological state that we observe in YbB6 is due to an inversion between Yb d and B p bands. These experimental and theoretical results provide a new approach for realizing novel correlated topological insulator states in rare-earth materials

Non-Kondo-like Electronic Structure in the Correlated Rare-Earth Hexaboride YbB6.
Published in Madhab Neupane, S.-Y. Xu, N. Alidoust, et al., Phys. Rev. Lett. 114, 016403 (2014).