A soft X-ray approach to electron-phonon interactions beyond the Born-Oppenheimer approximation

▶ We review modern soft X-ray methods to study electron-phonon coupling. ▶ Selection rules in X-ray emission enable the access to coupling rates. ▶ Band renormalizations can be analyzed with X-ray spectroscopy. ▶ Vibronic excitations are directly probed with high resolution X-ray spectroscopy. ▶ Strong phononic excitations are studied through X-ray emission after optical pumping.