Experimental time-resolved photoemission andab 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 Ybquantum-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 oftime-resolved two-photon photoemission spectroscopy (TR-2PPE). In particular, we showthat in spite of a seeming disagreement with the TR-2PPE measurements, theinelastic lifetimes yielded in STS experiments are close to the inelastic lifetimes ofbulk states, emphasizing the complementarity of both methods. Our approach issupported by ab initio electron self-energy calculations performed within the GW andGW+T approximations. Moreover we analyze the impact of the 4f-states on the lifetimes. We showthat the GW-term of the inverse lifetime (linewidth) is markedly smaller than theexperimental linewidth. The agreement with experimental data is recovered when theT-matrix is included in the linewidth calculations.