Inelastic light scattering at high-energy excitations in doped cuprate superconductors

Abstract

We present Raman spectra of low- and high-energy spin and charge excitations from ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ and ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}$ thin films as well as from ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ single crystals. We show that a rearrangement of spectral weight in ${B}_{1g}$ and ${A}_{1g}$ symmetry occurs below the respective critical temperatures ${T}_{c}$ of the samples at energies of about 5--6 times $2\ensuremath{\Delta}$, where $\ensuremath{\Delta}$ is the magnitude of the superconducting order parameter. The redistribution of spectral weight shifts with doping towards lower energies. For optimally doped samples strong renormalization effects of the electronic and phononic structures occur. We discuss our results in terms of a simplified $t\ensuremath{-}J$ model having magnetic and chargelike scattering channels. As far as the magnetic response is concerned, we apply the Heisenberg model of antiferromagnetism including self-energy contributions to the one-magnon states. This shows that the rearrangement at least partly results from an interaction between the remaining antiferromagnetism and the superconductivity. Moreover, the chargelike response at high energies seems to be influenced by the superconducting transition as well, indicating a strong interplay between holes and magnons in the normal and superconducting state.