Intraband transitions in simple metals: Evidence for non-Drude-like near-IR optical properties

By combining optical methods with photoelectron spectroscopy on crystalline AuIn2 films, clear evidence is provided for a non-Drude-like behavior of the intraband contribution to the optical response. The deviation from simple Drude theory is related to a non-free-electron-like density of states, which differs from the standard band shape assumed in the calculation of intraband excitations in ordered simple metals. The close connection between intraband optical and electronic properties is supported by results from amorphous AuIn2 films, for which a free-electron behavior is consistently observed by both methods.