# Electromagnetic properties of impure superconductors with pair-breaking processes

## TL;DR

This paper develops a comprehensive model to analyze the optical conductivity of gapless superconductors with impurities, revealing distinctive optical features and fitting recent experimental data on MoN films.

## Contribution

It introduces a unified approach to calculate optical conductivity in Dynes superconductors across all disorder regimes, extending existing theories.

## Key findings

- Identification of two optical absorption edges.
- Finite low-frequency absorption at low temperatures.
- Good fit to experimental data on MoN films.

## Abstract

Recently a generic model has been proposed for the single-particle properties of gapless superconductors with simultaneously present pair-conserving and pair-breaking impurity scattering (the so-called Dynes superconductors). Here we calculate the optical conductivity of the Dynes superconductors. Our approach is applicable for all disorder strengths from the clean up to the dirty limit and for all relative ratios of the two types of scattering, nevertheless the complexity of our description is equivalent to that of the widely used Mattis-Bardeen theory. We identify two optical fingerprints of the Dynes superconductors: (i) the presence of two absorption edges and (ii) a finite absorption at vanishing frequencies even at the lowest temperatures. We demonstrate that the recent anomalous optical data on thin MoN films can be reasonably fitted by our theory.