We report high resolution Angle Resolved PhotoElectron Spectroscopy (ARPES)
results on the (001) cleavage surface of YbB6, a rare-earth compound which
has been recently predicted to host surface electronic states with topological
character. We observe two types of well-resolved metallic states, whose Fermi
contours encircle the time-reversal invariant momenta of the YbB6(001)
surface Brillouin zone, and whose full (E,k)-dispersion relation can be
measured wholly unmasked by states from the rest of the electronic structure.
Although the two-dimensional character of these metallic states is confirmed by
their lack of out-of-plane dispersion, two new aspects are revealed in these
experiments. Firstly, these states do not resemble two branches of opposite,
linear velocity that cross at a Dirac point, but rather straightforward
parabolas which terminate to high binding energy with a clear band bottom.
Secondly, these states are sensitive to time-dependent changes of the YbB6
surface under ultrahigh vacuum conditions. Adding the fact that these data from
cleaved YbB6 surfaces also display spatial variations in the electronic
structure, it appears there is little in common between the theoretical
expectations for an idealized YbB6(001) crystal truncation on the one
hand, and these ARPES data from real cleavage surfaces on the other.Comment: 8 pages, 4 figures (accepted in Physical Review B