Identifying Su-Schrieffer-Heeger electron-phonon coupling in Resonant inelastic X-ray scattering experiments*

Resonant inelastic X-ray scattering (RIXS) is a powerful tool for studying the interplay between different degrees of freedom in strongly correlated materials. The method has been used extensively in the past in the study of electron-phonon (e-ph) coupled systems. We investigate the ability of RIXS to probe e-ph interactions in the Hubbard-SSH model in one dimension. The model combines the electronic correlations of the Hubbard model with the SSH model, which describes the modulation of electron hopping by the lattice vibrations.  In our RIXS study with the density matrix renormalization group for a half-filled Hubbard SSH model, we explore the effect of onsite Hubbard interaction and e-ph coupling on x-ray absorption spectroscopy and RIXS spectra. We find that the excitation of the lattice inevitably alters the electronic sector, causing the phonon peaks to soften in the RIXS spectra relative to their bare energy. Our study suggests a method to identify the presence of SSH-like interactions in strongly correlated quantum materials, thus broadening our understanding of the underlying mechanisms at play in such systems.