Fig. 1.

Electronic structure of the EuSn₂P₂ (001) surface. (A) Hard sphere representation of the crystal and magnetic structure of EuSn₂P₂, with the A-type antiferromagnetic arrangement of Eu spins indicated by the arrows. The gray line indicates the extension of thickness corresponding to the surface calculation in C and D, whereas the orange line marks the extension of the vertical axis of the unit cell. (B) Bulk rhombohedral and corresponding 2D-projected hexagonal Brillouin zone with high symmetry lines, arising from the $R\overline{3}m$ symmetry space group. (C and D) Symmetry resolved theoretical bulk- (Left) and surface-only (Right) band structure, respectively in the $\overline{\mathrm{\Gamma }}-\overline{K}$ and $\overline{\mathrm{\Gamma }}-\overline{M}$ directions, showing the contribution of Eu and P. The position of the Fermi level has been fixed to match the experimentally measured one. Each surface state is plotted with a color corresponding to the integrated charge density of the state within the topmost two EuSn₂P₂ unit blocks as indicated in A. (E and F) ARPES maps along the $\overline{\mathrm{\Gamma }}-\overline{K}$ and $\overline{\mathrm{\Gamma }}-\overline{M}$ directions, measured at $h\nu$ = 27 eV (respectively at T = 15 K and T = 80 K). (G and H) Magnified high-resolution maps of the dispersion near E_F; the extra bands (σ and P) are highlighted. Momentum distribution curve (MDC) and EDC are the blue and purple solid lines, respectively, in the top and side panels. (I) From top to bottom: calculated k_x − k_y isoenergetic Fermi surface for P-terminated surface; experimental k_x − k_y isoenergetic Fermi surface maps for P-terminated ($h\nu$ = 27 eV and T = 15 K) and non–P-terminated surface ($h\nu$ = 35 eV and T = 77 K); experimental MDC cuts along k_x axis ($\overline{\mathrm{\Gamma }}-\overline{K}$ direction), corresponding to, respectively, red and gray dashed lines for the two different terminations, with the extra bands $\sigma$ and $P$ indicated, as well as the $\alpha$ bulk band. The presence of different terminations has been verified by moving the light spot across the sample surface and monitoring changes of band structure around the Fermi level. The P termination was identified by comparison with calculations.