Natural linewidth of the Ag(111) L-gap surface state as determined by photoemission spectroscopy

The Ag(111) surface state in the L gap has been measured at T=30 K by high- resolution photoemission spectroscopy (Delta E=3.7 meV). The experimental l inewidth (full width at half maximum) at normal emission is less than 10 me V, from which an internal lifetime width of the surface states of Gamma(tot )=6.2+/-0.5 meV is deduced. This value agrees with theoretical predictions but is smaller than the result obtained by a recent low-temperature scannin g tunneling experiment, which gave a lifetime width equivalent to Gamma=9.8 +/-1.2 meV.