Energy conversion pathways in graphite from attosecond X-ray spectroscopy*

The conversion of light to fundamental excitations of matter is governed by the build-up of electronic coherences and their dephasing to excited quasiparticles due to scattering processes, which occur on atto- and femtosecond timescales. Disentangling the interplay of these mechanisms, and how they lead to a specific flow of energy inside a material, is extremely challenging since many of these effects occur on overlapping temporal scales. I will discuss the semimetal graphite which was investigated with attosecond K-shell X-ray absorption near edge structure (XANES) spectroscopy and how the combination of the measurement with theoretical modeling allows to assign the spectroscopic signatures to microscopic processes relating to the dynamic evolution of electrons, holes and phonon modes of the material. At the earliest times, already during photogeneration of carriers, we observe a competition between different carrier scattering effects and the excitation of strongly coupled optical phonons. Further, we elucidate the mechanism behind the excitation of SCOPs in graphite and their deexcitation. These measurements show the utility of our methodology even for a seemingly well-studied system like graphite for which it reveales novel insight and addresses standing questions. Since the method is generally applicable to molecules and solids, we expect it may prove valuable to address questions such as what the energy dissipation is in light-harvesting or energy storage systems, or to re-examine long-standing questions in non-equilibrium multi-body physics such as phase-transitions or superconductivity.