Extended Drude Model Analysis of the Optical Spectra of Correlated Electron Systems in a d-Wave Superconducting State

Correlation information in strongly correlated electron systems can be obtained using an extended Drude model. An interesting method related to the extended Drude model analysis of superconducting optical data was proposed recently. This method aims to extract the optical self-energy of quasiparticles (or residual unpaired electrons) from measured optical data in the superconducting state. However, this new optical self-energy is part of the (full) optical self-energy. The interpretation and the significance of this new optical self-energy is unclear. We investigate the proposed method by using a reverse process with simple electron-boson spectral density functions. With our obtained results, we conclude that the new optical self-energy is difficult to interpret because it provides an unphysical feature, which is a negative (optical) effective mass. The present study clarifies the extended Drude analysis method for superconducting optical data of correlated electron systems.