| Details: |
Superconductors (SCs) were one of the earliest materials that were investigated to study the purely electronic charge response due to inelastic scattering of light. This is because, the electronic Raman spectrum (eRS) usually yields a null result in single-band systems. The finite response in SCs was made possible because the excitation spectrum in a superconductor resembles that of a 2-band system. Nevertheless, it was almost always treated within a mean-field treatment where the eRS was expected to show absorption beyond the ‘inter-band’ gap. In this talk, I will demonstrate that this reasoning is not always sound, it does not reproduce experimental data, and even violates gauge invariance. These shortcomings are due to ignoring of the role of electronic correlations. In this talk, we will see that accounting for them addresses all the problems above and can also be extended to multiband systems. We will also see how eRS could be used to track phase transitions in the superconducting phase including spontaneous time reversal symmetry breaking such as in s+id and s+is states proposed and even detected in some recent unconventional SCs. |