Probing light-driven quantum materials with ultrafast resonant inelastic X-ray scattering

Ultrafast optical pulses are an increasingly important tool for controlling quantum materials and triggering novel photo-induced phase transitions. Understanding these dynamic phenomena requires a probe sensitive to spin, charge, and orbital degrees of freedom. Time-resolved resonant inelastic X-ray scattering (trRIXS) is an emerging spectroscopic method, which responds to this need by providing unprecedented access to the finite-momentum fluctuation spectrum of photoexcited solids. In this Perspective, we briefly review state-of-the-art trRIXS experiments on condensed matter systems, as well as recent theoretical advances. We then describe future research opportunities in the context of light control of quantum matter. Interrogating emergent nonequilibrium phenomena in light-driven quantum materials requires probing microscopic spin, charge and orbital excitations at ultrafast timescales. In this Perspective, time-resolved resonant inelastic X-ray scattering is discussed as a nascent method to investigate photoinduced states of matter.