Polarizability and single particle spectra of two-dimensional s- and d-wave superconductors

TL;DR

This paper analytically investigates the polarizabilities and single particle spectra of 2D s- and d-wave superconductors, predicting a collective charge mode observable via scattering experiments and explaining features seen in photoemission data.

Contribution

It provides new analytical results for polarizabilities in superconductors and predicts a collective charge mode below twice the gap energy, linking theory to experimental observations.

Findings

Existence of a collective charge mode below 2Δ energy.

Unusual features in single particle spectra due to scattering by collective modes.

Predictions applicable to inelastic scattering experiments.

Abstract

We present analytic results for the polarizabilities, $\chi({\bf Q},\omega)$, in the charge, spin, and current channels for two-dimensional s- and d-wave superconductors for large momentum transfer. A collective mode in the charge channel is predicted to exist for extremum vectors of the Fermi-surface with energy below twice the maximum superconducting gap. Such modes are directly observable through inelastic x-ray or electron scattering. Scattering of single particle excitations by these collective modes leads to several unusual features in the single particle spectrum in the superconducting state which are seen in angle resolved photoemission experiments.