Renormalization of electronic energy scales by electron-phonon interactions in the spin-chain cuprate Li$_2$CuO$_2$*

Recent advances in resonant inelastic x-ray scattering has improved energy resolution to the point that phonon excitations are now regularly observed in low-dimensional correlated materials. This observation provides a new way to study the electron-phonon interaction in these materials. I will discuss the observations of phonon excitations in the quasi-1D spin-chain cuprate Li$_2$CuO$_2$. Through detailed modeling of the RIXS spectra over a wide energy range we are able to determine the strength of this interaction. Importantly, we are also able to determine how several fundamental electronic energy scales such as the charge transfer energy and Cu-Cu exchange coupling are renormalized by interactions with the lattice. Our results point to the strong interplay between the lattice, charge, and magnetic excitations in Li$_2$CuO$_2$ and other low-dimensional cuprates. Ref: S. Johnston {\em et al}., Nature Commun. {\bf 7}, 10563 (2016).