OBSERVATION OF PHOTOEMISSION LINE WIDTHS NARROWER THAN THE INVERSE LIFETIME

Quantum mechanics stipulates that experimental spectral lines cannot b e narrower than the inverse lifetime. However, this limitation can be overcome in angle-resolved photoemission, and we have observed unusual ly narrow photoemission peaks derived from a bulk valence band of Ag. This observation is made possible by judiciously choosing a grazing em ission geometry to reach a specific tune ill tile reciprocal space, wh ere the final-state lifetime effect is suppressed, and simultaneously the initial-state lifetime contribution is kinematically compressed.