Angle-resolved Photoemission Spectroscopy Study on the Surface States of the Correlated Topological Insulator YbB6

YbB6 is recently predicted to be a moderately correlated topological insulator, which provides a playground to explore the interplay between correlation and topological properties. With angle-resolved photoemission spectroscopy, we directly observed almost linearly dispersive bands around the time-reversal invariant momenta (Gamma) over bar and (X) over bar with negligible k(z) dependence, consistent with odd number of surface states crossing the Fermi level in a Z(2) topological insulator. Circular dichroism photoemission spectra suggest that these in-gap states possess chirality of orbital angular momentum, which is related to the chiral spin texture, further indicative of their topological nature. The observed insulating gap of YbB6 is about 100 meV, larger than that found by theoretical calculations. Our results present strong evidence that YbB6 is a correlated topological insulator and provide a foundation for further studies of this promising material.