Extracting the dynamical effective interaction and competing order from an analysis of Raman spectra of the high-temperature La2-xSrxCuO4 superconductor

We discuss the problem of the glue mediating the effective electron-electron interaction and the related order underlying superconductivity in the cuprates. Assuming as mediators spin and charge fluctuations with different characteristic wavevectors, we calculate the Raman response function including self-energy and vertex corrections. In this way, exploiting the related cancellations, we are able to individuate the charge and spin contributions in the Raman response function. Raman scattering experiments in La2-xSrxCuO4 single crystals have been systematically carried out at various doping levels x. By fitting the experimental spectra within the above theoretical framework, we find a charge and spin nearly ordered state, whose fluctuations give rise to a spin dominated glue function at intermediate doping and a charge dominated one above optimal doping.