Coupled Electronic and Structural Evolution in Materials Probed by Tabletop Femtosecond Coherent XUV Absorption Spectroscopy.

Understanding the coupled dynamics of electronic, spin, and lattice degrees of freedom in solids is essential for advancing energy conversion, information processing, and emerging quantum technologies. However, directly resolving these interactions at the atomic scales on their intrinsic femtosecond time scales is a challenge. Here, we describe recent advances of laboratory-based coherent extreme ultraviolet (XUV) and soft X-ray light sources that enable atom-specific probing of coupled electronic, structural, and spin dynamics across diverse material systems. We provide a comprehensive technical overview of spectroscopic developments, including source generation, time-resolved beamline design, and experimental geometries. We present representative examples demonstrating how core-to-valence transitions enable time-resolved XUV/soft X-ray spectroscopy to provide element-, site-, and spin-specific sensitivity to lattice distortions coupled to charge-transfer states, lattice-driven spin transitions, and coherent phonon-mediated phase transformations. These capabilities are therefore expanding our understanding of vibronic and spin-vibronic phenomena from molecules to complex materials systems. We conclude by outlining key challenges and future opportunities in this field, including spectroscopic developments, and elucidating deeper insight into nonequilibrium phenomena in complex quantum and functional materials.