Quasiparticle Lifetime in Macroscopically Uniform Ag/Fe(100) Quantum Wells

Epitaxial Ag(100) films have been grown on highly perfect Fe(100) substrates by deposition at low temperatures followed by annealing. Precise control of the deposition process results in film thicknesses of exactly $N$ atomic layers ( $N$ an integer up to 39) over a macroscopic distance $\left(\sim 1\mathrm{mm}\right)$. The elimination of atomic layer fluctuation, which has been generally believed to be impossible at such large thicknesses, allows us to observe atomic-layer resolved quantum well states. Such states exhibit extremely narrow linewidths, which provide a direct measure of the quasiparticle lifetime.