Resonant two‐magnon Raman scattering in high‐T_c cuprates

Abstract

Resonance enhancement of one-phonon, two-phonon, and two-magnon Raman scattering in a general, exactly solvable, multiband model is explained in a way that is in accordance with the general analytical properties of the total optical conductivity tensor. Using this approach, the charge-transfer limit of the Emery three-band model is examined to explain resonance enhancement of the two-magnon Raman spectra of high-T c cuprates, which is found in experiments to be of 3 orders of magnitude. While previous Raman and optical conductivity analyzes of the cuprates, based on the single-band Hubbard model, are found to be consistent with the picture where one hole per one CuO 2 unit is localized on the Cu ion, the present three-band approach allows the study of the opposite, strong copper-oxygen hybridization limit, which is found to be in agreement with the results of nuclear magnetic resonance (NMR) and one-phonon Raman scattering experiments. Copyright

Triple‐resonant two‐phonon Raman scattering in graphene

“…Here, δt ν (q) = (g ν / √ N)u νq is the product of the phonon field u νq and the electron-phonon coupling constant g ν / √ N (e ν q is the related polarization vector, and u a νq = −u b νq ≡ u νq ). [5,19] Furthermore,…”

“…(Refs [2,5]) and Eqn (1) for the interband optical conductivity, we obtain four contributions to the photon-two-phonon coupling function T νν,αα (ω i ), corresponding to four terms in the factor…”

“…The Emery threeband model for cuprate superconductors is the typical example where this happens for usual laser energies. [5] …”

“…These effects are explained within a multiband electronic model with relatively complicated band dispersions by treating the doubleresonant (DR) and triple-resonant (TR) scattering processes on equal footing. [4,5] A closely related effect is the laser energy dependence of the position of the disorder-induced D band and the corresponding second-order G band in different sp 2 -based carbon materials. [6 -12] Physical grounds for the dispersive behavior of these two Raman signals in graphite have been explained by Thomsen and Reich (Ref.…”