Electron-boson glue function derived from electronic Raman scattering

TL;DR

This study extracts electron-boson spectral densities from Raman scattering data in cuprates, comparing them with ARPES and optical results, revealing momentum-dependent features and scattering processes relevant to high-temperature superconductivity.

Contribution

It introduces a modified maximum entropy inversion technique to derive electron-boson spectral densities from Raman data, enabling direct comparison with ARPES and optical measurements.

Findings

$B_{2g}$ spectrum aligns with nodal ARPES data

$B_{1g}$ spectrum resembles optical spectrum

A peak at 30-40 meV suggests $(\pi,\pi)$ scattering importance

Abstract

Raman scattering cross sections depend on photon polarization. In the cuprates nodal and antinodal directions are weighted more strongly in $B_{2g}$ and $B_{1g}$ symmetry, 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. In contrast, the optical conductivity involves a momentum average over the entire Brillouin zone. Newly measured Raman response data on high-quality Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ single crystals up to high energies have been inverted using a modified maximum entropy inversion technique to extract from $B_{1g}$ and $B_{2g}$ Raman data corresponding electron-boson spectral densities (glue) are compared to the results obtained with known ARPES and optical inversions. We find that the $B_{2g}$ spectrum agrees qualitatively with nodal direction ARPES while the $B_{1g}$ looks more like the optical spectrum. A large peak around $30 - 40\,$meV in $B_{1g}$, much less prominent in $B_{2g}$, is taken as support for the importance of $(\pi,\pi)$ scattering at this frequency.