How Electrons and Atoms Can Dance Out of Sync: Insights from Attosecond Core-Level Spectroscopy

»Attosecond spectroscopy allows us to watch how electrons move and interact with atoms in real time. Using ultrashort laser pulses, we can see electrons localize around specific atoms within a few femtoseconds and how these motions influence the surrounding lattice. By studying materials such as titanium, tungsten, MoSe2, and MXenes, we find that electrons and atoms can briefly fall out of sync: electrons respond about 30 fs later than the vibrating atoms in MXenes. This ›delay‹ reveals a breakdown of the Born–Oppenheimer approximation, which normally assumes that electrons instantly follow atomic motion. These results open a new window into how energy flows and transforms inside materials.«

— Ursula Keller