Unravelling the glue and the competing order in superconducting cuprates

TL;DR

This study uses Raman scattering to analyze how spin and charge fluctuations contribute to superconductivity in cuprates, revealing a doping-dependent shift from spin to charge dominance in pairing interactions.

Contribution

It provides experimental evidence for the doping-dependent evolution of the pairing glue, highlighting the role of spin and charge fluctuations in cuprate superconductors.

Findings

Spin fluctuations dominate at low doping.

Charge fluctuations become dominant near optimal doping.

Fluctuations support the coexistence of spin and charge order in pairing.

Abstract

We present Raman scattering experiments in ${\rm La_{2-x}Sr_xCuO_4}$ single crystals at various doping levels x and compare the results with theoretical predictions obtained assuming an interaction mediated by spin and charge fluctuations. The light-scattering selection rules allow us to disentangle their respective contributions. We find that the glue spectral function is spin-dominated at low doping while the contribution of charge fluctuations becomes dominant around optimal doping. This indicates that the fluctuations of a nearly ordered state with coexisting spin and charge order support the superconducting pairing.