Quantum-well states above the Fermi energy in thin Yb(111) metal films deposited on a W(110) single crystal were studied by low-temperature scanning tunneling spectroscopy. These states are laterally highly localized and give rise to sharp peaks in the tunneling spectra. A quantitative analysis of the spectra yields the bulk-band dispersion in the $\Gamma \mathrm{\text{−}}L$ direction as well as quasiparticle lifetimes. The quadratic energy dependence of the lifetimes is in quantitative agreement with Fermi-liquid theory.

• Received 8 November 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.126804