Resonant inelastic soft x-ray scattering as a site-specific probe of electron-phonon coupling in one-dimensional edge-shared cuprates

Resonant inelastic x-ray scattering (RIXS) is a powerful probe for studying excitations in strongly correlated systems. With continued advancements of the technique the overall energy resolution has improved to the point of probing low-energy boson excitations near the elastic line. In this talk we present evidence for coupling to an optical oxygen phonon in the RIXS spectrum at the oxygen K-edge of the quasi-1D edge shared cuprate Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$. This mode is identified as a compressive mode polarized perpendicular to the chain direction, modulating the Cu-O charge transfer energy and setting the size exchange interaction. By comparing to small cluster calculations we extract a sizable electron-phonon coupling strength in a site-resolved manner, implying a strong integration of the lattice degrees of freedom into the electronic structure.