Figure 1: Experimental and theoretical insight into the 4f-derived electron structure.

ARPES data of (a) Si- and (b) Eu-terminated surfaces are shown in a colour representation where yellow (red) denotes the largest photoemission intensity. The data were taken at 120 eV photon energy, that is, sensitive to 4f emissions while signals from Rh 4d states are strongly suppressed by cross-section effects. Note that Eu termination is concluded from the presence of Eu 4f surface signals between 1.1 and 1.9 eV BE, whereas the lack of such signals indicates Si termination because the bonding between Si and Rh atoms is tight and cleavage takes place prediominantly between Eu and Si layers (see Supplementary Fig. S2). Modelled ARPES spectra of respective terminations are presented in c and d. Note that only the 4f admixtures to the bands are plotted, whereas the experimental data reveal weak contributions from states of other symmetries also.