Lifetimes of image-potential states on copper surfaces

The lifetime of image states, related to the coupling of surface electronic states with the solid substrate, has been recently determined for quantum numbers n less than or equal to 6 on Cu(100) by using time-resolved two-photon photoemission in combination with the coherent excitation of several states [U. Hofer et nl., Science 277, 1480 (1997)]. We evaluate the lifetimes of image states on copper surfaces from the self-energy of the excited quasiparticle, which we compute within the GW approximation. Single-particle wave functions are obtained by solving the Schrodinger equation with a realistic one-dimensional model potential, and the screened interaction is evaluated in the random-phase approximation. Our results are in agreement with experimentally determined decay times.