Non-Kondo-like electronic structure in the correlated rare-earth hexaboride Yb B6

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 like surface states enclosing the Kramers's points, while the f orbital that would be relevant for the Kondo mechanism is ∼1eV 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.