An electron-boson glue function derived from electronic Raman scattering

Raman scattering cross sections depend on photon polarization. In the cuprates, nodal and antinodal directions are weighted more strongly in B2g and B1g symmetries, respectively. On the other hand, in angle-resolved photoemission spectroscopy (ARPES), electronic properties are measured along well-defined directions in momentum space rather than their weighted averages being taken. In contrast, the optical conductivity involves a momentum average over the entire Brillouin zone. Newly measured Raman response data on high-quality Bi2Sr2CaCu2O8+δ single crystals up to high energies have been inverted using a modified maximum entropy inversion technique to extract from B1g and B2g Raman data corresponding electron-boson spectral densities (glue), and these are compared to the results obtained with known ARPES and optical inversions. We find that the B2g spectrum agrees qualitatively with nodal direction ARPES while the B1g results look more like the optical spectrum. A large peak around 30-40 meV in B1g and a much less prominent one in B2g are taken as support for the importance of (π, π) scattering at this frequency.