Charge-fluctuation contribution to the Raman response in superconducting cuprates

TL;DR

This paper investigates how charge fluctuations contribute to the Raman response in superconducting cuprates, revealing polarization and wavevector dependencies that align with experimental observations of low-energy peaks.

Contribution

It provides a theoretical calculation of the Raman response from charge collective modes, explaining experimental features in underdoped cuprates.

Findings

Charge collective modes cause polarization-dependent Raman peaks.

Low-energy peaks soften with decreasing temperature.

Results match experimental doping and polarization dependence.

Abstract

We calculate the Raman response contribution due to collective modes, finding a strong dependence on the photon polarizations and on the characteristic wavevectors of the modes. We compare our results with recent Raman spectroscopy experiments in underdoped cuprates, $La_{2-x}Sr_xCuO_4$ and $(Y_{1.97}Ca_{0.3})Ba_2CuO_{6.05}$, where anomalous low-energy peaks are observed, which soften upon lowering the temperature. We show that the specific dependence on doping and on photon polarizations of these peaks is only compatible with charge collective excitations at finite wavelength.