Extended Drude model analysis of noble metals

We have applied the extended Drude model (EDM) to noble metals of Cu, Ag, and Au. Drude parameters are obtained self‐consistently without using the sum rule or any approximation. The core polarization contribution ε∞ is shown to be large due to shallow d‐orbitals. The frequency dependent mass enhancement factor λ (ω) and the scattering rate 1/τ (ω) are obtained. The Drude region can be identified when 1/τ (ω) deviates from the Fermi liquid behavior due to interband transitions. The onset frequency for the interband transition is found to be lower than the frequency value at the minimum of the imaginary part of the dielectric constant. The validity of the approximation of ωτ ≫ 1, which is commonly employed in analyzing optical data, has been checked based on the EDM for noble metals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)