Experimental time-resolved photoemission and ab initio GW + T study of lifetimes of excited electrons in ytterbium

Abstract

In this paper we give a detailed analysis of the difference between the lifetimes of Yb quantum-well states measured by scanning tunneling spectroscopy (STS) in Wegner et al (2005 Phys. Rev. Lett. 94 126804) and the lifetimes of bulk Yb obtained by means of time-resolved two-photon photoemission spectroscopy (TR-2PPE). In particular, we show that in spite of a seeming disagreement with the TR-2PPE measurements, the inelastic lifetimes yielded in STS experiments are close to the inelastic lifetimes of bulk states, emphasizing the complementarity of both methods. Our approach is supported by ab initio electron self-energy calculations performed within the GW and GW+T approximations. Moreover we analyze the impact of the 4f-states on the lifetimes. We show that the GW-term of the inverse lifetime (linewidth) is markedly smaller than the experimental linewidth. The agreement with experimental data is recovered when the T-matrix is included in the linewidth calculations.