Angle-resolved Photoemission Spectroscopy Study on the Surface States of the Correlated Topological Insulator YbB 6

YbB 6 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 and 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 YbB 6 is about 100 meV, larger than that found by theoretical calculations. Our results present strong evidence that YbB 6 is a correlated topological insulator and provide a foundation for further studies of this promising material.