Transient extreme ultraviolet spectroscopy: a probe of ultrafast charge dynamics in solid-state materials

Abstract

Over the past two decades, transient extreme ultraviolet spectroscopy (Tr-XUV) has evolved into a unique probe of ultrafast electronic dynamics. In this review, we summarize several advances and applications of this technique to study solid-state materials. We first discuss how this technique enables understanding of small polaron formation in varying chemical environments, a central application in the early development of the technique. We then describe emerging directions where Tr-XUV has provided distinctive insight, including charge transfer across interfaces and charge localization through giant resonances. Lastly, we discuss instances where its combination with other ultrafast spectroscopies facilitates a more complete physical picture. Together, these advances demonstrate that ultrafast core-level spectroscopy in the extreme ultraviolet regime reveals a comprehensive framework for nonequilibrium dynamics that establishes it as a versatile frontier technique for materials science.