ARPES insights on the metallic states of YbB6(001): E(k) dispersion, temporal changes and spatial variation

TL;DR

This study uses high-resolution ARPES to investigate the surface electronic states of YbB6(001), revealing non-Dirac parabolic metallic states that vary with time and space, challenging idealized theoretical models.

Contribution

It provides new experimental insights into the surface states of YbB6(001), showing they are parabolic, time-sensitive, and spatially variable, unlike the Dirac-like states predicted by theory.

Findings

Metallic states are parabolic, not Dirac-like.

Surface states show temporal changes under ultrahigh vacuum.

Spatial variations indicate deviations from idealized models.

Abstract

We report high resolution Angle Resolved PhotoElectron Spectroscopy (ARPES) results on the (001) cleavage surface of YbB$_{6}$, 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 YbB$_{6}$(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 YbB$_{6}$ surface under ultrahigh vacuum conditions. Adding the fact that these data from cleaved YbB$_{6}$ surfaces also display spatial variations in the electronic structure, it appears there is little in common between the theoretical expectations for an idealized YbB$_{6}$(001) crystal truncation on the one hand, and these ARPES data from real cleavage surfaces on the other.