Collective modes in singlet superconductors

TL;DR

This paper discusses the classification and characteristics of collective excitation modes in singlet superconductors, focusing on their symmetry properties and how they couple to charge density, phase, and amplitude fluctuations.

Contribution

It provides a systematic classification of collective modes in singlet superconductors based on symmetry representations and their coupling behaviors.

Findings

Classification of collective modes by irreducible representations

Analysis of coupled charge density and phase excitations

Identification of amplitude mode characteristics

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 $\rho$ and the phase $\phi $ of the order parameter, or of the amplitude $\Delta$ 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 $L$.