Two-dimensional band structure and self-energy of Bi(111) near theΓ¯point

Angle-resolved photoemission spectroscopy with synchrotron radiation was used to map the Fermi surface and the dispersion of the associated bands of Bi(111) near the $\overline{\Gamma }$ point. Using variable photon energies we prove the two-dimensional nature of these bands. From fits of the spectral function $A(\omega ,k)$ to momentum distribution curves of the hole band we determined the imaginary part of the electron self-energy $\mathrm{Im}\Sigma \left(\omega \right).\mathrm{}$ The small energy dependence of $\mathrm{Im}\Sigma \left(\omega \right)$ near the Fermi level, which can be explained by electron-phonon interactions, indicates nonquasiparticle behavior. By means of a Hilbert transform of $\mathrm{Im}\Sigma \left(\omega \right)$ we extract the energy dependence of $\mathrm{Re}\Sigma \left(\omega \right).\mathrm{}$ Based on the bulk Debye phonon model we determine the electron-phonon coupling constant $\lambda =0.6\mathrm{}\pm 0.05$