Photoemission Study of a Strongly Coupled Electron-Phonon System

We present high-resolution photoemission experiments of the $\overline{\Gamma }$-surface state of Be(0001). The spectral function near the Fermi wave vector reveals a strong quasiparticle peak due to coupling with surface phonon modes. The coupling constant $\lambda$ is estimated to be $1.18\pm 0.07$ based on the renormalization of the effective mass. No gap was observed down to 12 K. Any interpretation of the data based on charge density wave formation or surface superconductivity can therefore be discarded.