Abstract :
Linewidths of direct transitions as observed by angle resolved photoemission are determined by the initial and final state lifetime widths as well as the experimental geometry. The geometry plays a role because conservation of momentum within the surface plane places a constraint on the allowed transition. This effect can lead to either a compression or expansion of the measured linewidth. This paper addresses ways to suppress the final state lifetime contribution, which is usually much larger and dominant, and simultaneously to compress the initial state lifetime contribution. The result is a linewidth significantly narrower than the quasiparticle inverse lifetime, as demonstrated by an experiment involving the sp band of Ag(100).
