Systematic angle-resolved photoemission spectroscopy (ARPES) experiments have been carried out to investigate the bulk and (100) surface electronic structures of a topological mixed-valence insulator candidate, YbB6. The bulk states of YbB6 were probed with bulk-sensitive soft X-ray ARPES, which show strong three-dimensionality as required by cubic symmetry. Surprisingly the measured Yb 4f states are located around 1 eV and 2.3 eV below the Fermi level (EF), instead of being near EF as indicated by first principle calculations. The dispersive bands near EF are B 2p states, which hybridize with the 4f states. Using surface-sensitive vacuum-ultraviolet ARPES, we revealed two-dimensional surface states which form three electron-like Fermi surfaces (FSs) with Dirac-cone-like dispersions. The odd number of surface FSs gives the first indication that YbB6 is a moderately correlated topological insulator. The spin-resolved ARPES measurements provide further evidence that these surface states are spin polarized with spin locked to the crystal momentum. We have observed a second set of surface states with different topology (hole-like pockets). Clear folding of the bands suggest their origin from a 1X2 reconstructed surface. The topological property of the reconstructed surface states needs further studies.
@article{arxiv.1405.0165,
title = {Surface vs bulk electronic structures of a moderately correlated topological insulator YbB6 revealed by ARPES},
author = {N. Xu and C. E. Matt and E. Pomjakushina and J. H. Dil and G. Landolt and J. -Z. Ma and X. Shi and R. S. Dhaka and N. C. Plumb and M. Radovic and V. N. Strocov and T. K. Kim and M. Hoesch and K. Conder and J. Mesot and H. Ding and M. Shi},
journal= {arXiv preprint arXiv:1405.0165},
year = {2014}
}