Collective modes in singlet superconductors

Abstract

A brief summary of collective mode excitations that can exist in singlet superconductors with irreducible representation $L$ is given. Such excitations may be classified as the coupled excitations of the charge density $ρ$ and the phase $ϕ$ of the order parameter, or of the amplitude $Δ$ of order parameter. Each of these classes may be further characterized in the long wavelength limit by the irreducible representation $\ell$ of the excitation, which may or may not be the same as the ground state $L$.

An addendum to our earlier paper titled "Higgs modes in D-wave Superconductors"