Prize Talk: IUPAP Prize Winner: An X-ray view of light-driven quantum materials*

Over the last two decades, intense ultrashort electromagnetic fields have enabled observing and controlling a plethora of emergent states in quantum materials. Some of the most spectacular light-induced phenomena, such as superconducting-like phases, transient charge density wave ordering, and excitonic condensation, are found to occur in materials dominated by strong electronic correlations with a large susceptibility to external stimuli. To fully understand the microscopic physics of these dynamical states of matter, one needs to directly measure their transient electronic dynamics and effective interactions at fundamental time and length scales.

In this talk, I will discuss advances in ultrafast x-ray spectroscopic methods, such as time-resolved x-ray absorption (trXAS) and time-resolved resonant inelastic x-ray scattering (trRIXS). X-ray spectroscopy at free electron lasers enables probing quantum materials at microscopic scales and with element selectivity, thus providing an unprecedented view of light-induced phenomena in solids. I will particularly focus on light-driven Mott insulators, which are key to the emergence of light-induced superconductivity and are theoretically argued to host other exotic ordering phenomena upon photoexcitation, such as eta-pairing condensation. I will discuss how trXAS allows us to accurately determine transient effective electronic interactions, and to fully reconstruct the charge distribution of the driven many-body state. Further, I will discuss how trRIXS enables mapping the magnetic excitation spectrum at finite momentum and highlight the implications of these experiments for the realization of new light-induced states of matter.