The surfaces of bismuth: Structural and electronic properties

This paper reviews recent experimental and theoretical work on some low-index surfaces of the group V semimetal bismuth. The main focus is on the geometric and electronic structure, including the effect of the spin–orbit interaction, and on the electron–phonon coupling. The surface geometric structures of Bi(1 1 1), Bi(1 1 0) and Bi(1 0 0) do not undergo any dramatic changes with respect to the bulk structure but the electronic structure does: All three surfaces support metallic surface states with larger Fermi surface elements and generally lower Fermi velocities than the bulk states. Therefore the surfaces are considerably better metals than the bulk. This surface electronic structure can only be understood when the spin–orbit coupling is taken into account, which leads to a strong splitting of the fact that the surface state bands due to the loss of symmetry at the surface. The surface state bands contain only one electron per k point has a profound impact on effects such as screening and the possible formation of charge density waves. The strength of the electron–phonon interaction for the surface states of Bi is strongly energy dependent. At higher binding energies, where inter-band scattering with bulk states can be important, strong electron–phonon coupling can be observed (λ > 0.7). Close to the Fermi level, where only scattering within the surface state bands is relevant, the coupling is of intermediate strength with λ ≈ 0.2–0.4, depending on the surface and the particular state.