Abstract
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.
Highlights
Very recently, petahertz laser fields have enabled the possibility to drive fast currents in dielectric, semiconductor, and modern materials, opening the door to a new timescale for control in solid-state systems [1,2,3,4,5]
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
We show that ATAS changes around Van Hove points, i.e., points in the Brillouin zone (BZ) in which the density of states presents singularities, are directly associated with a coherent phase that electrons acquire during the dynamics driven by a petahertz laser field, and this phase contains the information of the semiclassical action
Summary
Petahertz laser fields have enabled the possibility to drive fast currents in dielectric, semiconductor, and modern materials, opening the door to a new timescale for control in solid-state systems [1,2,3,4,5]. An alternative pump-probe scenario for solid materials ( for gas-phase studies) currently under development in several laboratories consists of using an ultrashort IR pump pulse to excite the system and a single attosecond pulse to probe the pump-induced dynamics with a controlled time delay, see Fig. 1(a). In this scheme the IR-induced dynamics produces changes in the absorption of the attosecond pulse as a function of the pump-probe delay (attosecond transient absorption spectroscopy, ATAS). The semiclassical action is connected both to the local energy dispersion and the Berry connections of the conduction band This is just possible due to the special characteristics of attosecond x-ray pulses, which couple flat bands (core electrons) with the conduction and valence bands. The present work establishes a theoretical framework for ATAS and suggests that attosecond electron dynamics imprinted in ATAS could be used to develop unprecedented imaging techniques for modern materials
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