Surface electronic structure of bismuth oxychalcogenides

Within density functional theory we study the bulk band structure and surface states of bismuth oxychalcogenides ${\mathrm{Bi}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ and ${\mathrm{Bi}}_{2}{\mathrm{O}}_{2}\mathrm{Te}$. We consider both polar and nonpolar surface terminations. On the basis of relativistic ab initio calculations, we show that both unreconstructed (polar) and reconstructed (nonpolar) surfaces possess the Rashba spin-split surface states. The metallic Rashba-split states on polar surfaces stem from huge potential bending, positive or negative, depending on surface polarity. On the nonpolar surfaces resulting from single-crystal cleavage the emerging Rashba-split states are nonmetallic.