Phonon contribution to quasiparticle lifetimes in Cu measured by angle-resolved photoemission

Abstract

The line shape of the photoelectron spectrum emitted from the sp-derived surface state at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} on Cu(111) is investigated. The line shape is Lorentzian, and the temperature dependence of the width is linear, varying from 30 meV at 30 K to 75 meV at 625 K. Less than 5-meV variation with binding energy is observed. The temperature dependence is explained as the phonon contribution to the inverse hole lifetime, predicted to be 2\ensuremath{\pi}\ensuremath{\lambda}${\mathit{k}}_{\mathit{bT}}$ allowing the determination that the electron-phonon mass enhancement parameter \ensuremath{\lambda}=0.14\ifmmode\pm\else\textpm\fi{}0.02 for this surface state at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}. This is compared to \ensuremath{\lambda}=0.15 reported as an average over the bulk Fermi surface.