Electron-phonon coupling in photoemission spectra

Abstract

We present high-resolution photoemission data of the ⌫ -surface state on Be͑0001͒. Near the Fermi surface a narrow quasiparticle peak caused by strong electron-phonon coupling emerges. A many-body calculation is performed, which describes precisely the exceptional evolution of the experimental spectra. We demonstrate that all the necessary parameters can be directly deduced from the experiment. ͓S0163-1829͑99͒00236-2͔

Decay of electronic excitations at metal surfaces

“…Moreover, they demonstrate that all necessary parameters can be extracted from the experiment: l ¼ 1:18 and ho m ¼ 70 meV. Also a contribution of G def ¼ 75 meV is found, which translates into a mean free path of about 15 Å in the surface plane [142]. This value appears independent of E i , at least up to a distance of 0.6 eV from E F .…”

“…For more details on theory and the interpretation of Im S concerning the G surface states on noble metals see Section 6.1. An even larger contribution of S is to be expected for the surfaces of Be, where ho m ¼ 70 meV and the coupling parameter l on Be(0 0 0 1) is estimated between 0:7 AE 0:1 [126], 1.15 [140] and 1.18 [141,142]. Strong contribution to G ep is indeed observed and will be discussed in the following.…”

“…They determine the initial state energy E i ¼ À2:73 eV at G, and effective masses m à =m ¼ 1:19 (along GM) and m à =m ¼ 1:14 (GK). Hengsberger et al [141,142] demonstrated that the surface state is drastically modified near E F by the electron-phonon interaction. In particular, the lineshape near E F is no longer a Lorentzian: as the surface state approaches E F , a second peak appears at E i % À70 meV.…”

“…to the noble metals. Very highresolution lineshape results on the G surface state were presented first by Hengsberger et al [141,142], with data taken at T ¼ 12 K and resolution parameters DE ¼ 5 meV and Dy ¼ 0:2 (in the direction of strong dispersion), respectively. They determine the initial state energy E i ¼ À2:73 eV at G, and effective masses m à =m ¼ 1:19 (along GM) and m à =m ¼ 1:14 (GK).…”

“…The second quasiparticle peak is caused by the strong electron-phonon coupling. Using conventional many-body theory Hengsberger et al [142] describe precisely this exceptional double-peak evolution of the experimental spectra. Moreover, they demonstrate that all necessary parameters can be extracted from the experiment: l ¼ 1:18 and ho m ¼ 70 meV.…”