Authors: J.K. Freericks, T.P. Devereaux, and R. Bulla
Journal:
Acta Phys. Pol. B 34, 737 (2003)
Electronic Raman scattering has been employed to examine a number of different correlated insulators, including the high-temperature superconductors, Kondo insulators (like FeSi), and intermediate-valence compounds (like SmB6). The experimental data all share a number of common features: in the B1g channel (crossed polarizers) one finds (i) a sudden onset of low energy spectral weight transfered from a higher charge-transfer peak, which rapidly increases as T increases; (ii) the appearance of an isosbestic point (where the Raman response is independent of T) separating the regions where the spectral weight shifts; and (iii) a large ratio of the spectral range over which spectral weight increases as T increases (representative of the charge gap) to the onset temperature, where the gap appears to first open. We solve for the Raman response exactly using dynamical mean field theory for the Falicov-Kimball model and the Hubbard model. Our solutions illustrate all three of these experimental features. In addition, we calculate the inelastic light scattering from X-rays, which allows the photon to transfer both energy and momentum to the electronic charge excitations. We find that the charge transfer peak and the low energy peak both broaden and disperse through the Brillouin zone similar to what is seen in experiments in materials like Ca2CuO2Cl2.