Attosecond x-ray transient absorption spectroscopy in graphene

Real-time observations of the coherent electron dynamics induced by ultrashort light pulses in condensed-matter systems have remained elusive due to limitations in existing attosecond devices. Here we show that attosecond transient absorption resulting from an IR-pump/x-ray probe numerical experiment performed in graphene unambiguously encodes the information of the coherent electron dynamics induced by the pump pulse. First, we demonstrate the possibility of tracking in real time the electron injection through the Dirac points. Second, we derive and demonstrate a simple semiclassical theory that correlates the energy structure and the action Berry phase with strong changes in the absorption spectrum around Van Hove singularities. Our work opens the way to the development of novel imaging techniques in condensed matter systems at the attosecond timescale.