# Extended Drude model analysis of superconducting optical spectra of correlated electron systems

## TL;DR

This paper critically examines the extended Drude model analysis of superconducting optical spectra in correlated electron systems, revealing limitations and unphysical features in the residual optical self-energy interpretation.

## Contribution

It clarifies the interpretation of the extended Drude analysis method for superconducting optical data and highlights issues with residual optical self-energy.

## Key findings

- Residual optical self-energy contains unphysical features
- Negative optical effective mass observed in residual self-energy
- Clarifies limitations of the extended Drude analysis in superconductors

## Abstract

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, and it has attracted attention from researchers. 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 residual optical self-energy is a partial optical self-energy. The interpretation and significance of this partial optical self-energy is unclear. We investigate this method using a reverse process with simple electron-boson spectral density functions. With our obtained results, we conclude that the residual (or partial) optical self-energy is difficult to interpret because it contains unphysical features, in particular, a negative optical effective mass. The present study clarifies the extended Drude analysis method for superconducting optical data.