Attosecond electron dynamics in solid-state systems

Attosecond science has revolutionized the study of ultrafast electron dynamics. Originally based on high-order harmonic generation from intense laser fields, it provided groundbreaking insights into physical processes occurring on the few- to sub-femtosecond time scales. From its initial focus on atomic and molecular systems, the field rapidly expanded to solid-state materials, uncovering phenomena with possible significant implications for information technology. This review focuses on some of the key experimental techniques that enable attosecond resolution in solid-state systems. We categorize them into four main groups: core-hole clock spectroscopy, photoemission, XUV-based all-optical techniques, and sub-cycle strong-field approaches. Together, these methods contributed to significant breakthroughs, such as elucidating the timing of photoemission from solids, possibly enabling the manipulation of the electro-optical properties of a crystal with light fields, and advancing our understanding of fundamental light-matter interactions. Their application to novel materials and the development of innovative, cutting-edge light sources and techniques, will define the future of attoscience in solids, setting the basis for profound advancements in both scientific understanding and technological innovation.