Theoretical analysis of STM-derived lifetimes of excitations in the Shockley surface-state band of Ag(111)

We present a quantitative many-body analysis using the GW approximation of the decay rate Gamma due to electron-electron scattering of excitations in the Shockley surface state band of Ag(111), as measured using the scanning tunneling microscope (STM). The calculations include the perturbing influence of the STM, which causes a Stark-shift of the surface state energy E and concomitant increase in Gamma. We find Gamma varies more rapidly with E than recently found for image potential states, where the STM has been shown to significantly affect measured lifetimes. For the Shockley states, the Stark shifts that occur under normal tunneling conditions are relatively small, and previous STM-derived lifetimes need not be corrected.