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For interaction of light with condensed-matter systems, we show with simulations that ultrafast electron and X-ray diffraction can provide a time-dependent record of charge-density maps with sub-cycle and atomic-scale resolutions. Using graphene as an example material, we predict that diffraction can reveal localised atomic-scale origins of optical and electronic phenomena. In particular, we point out nontrivial relations between microscopic electric current and density in undoped graphene.

Ultrafast charge transfer processes from adsorbates to substrates are believed to occur on the timescale of (sub)-femtoseconds. In this paper we present experimental evidence for resonant tunneling of electrons at surfaces in the time regime ranging from

A wide range of ultrafast phenomena in various atomic, molecular and condense matter systems is governed by electron dynamics. Therefore, the ability to image electronic motion in real space and real time would provide a deeper understanding of such processes and guide developments of tools to control them. Ultrashort light pulses, which can provide unprecedented time resolution approaching subfemtosecond time scale, are perspective to achieve real-time imaging of electron dynamics. This task is challenging not only from an experimental view, but also from a theory perspective, since standard theories describing light-matter interaction in a stationary regime can provide erroneous results in an ultrafast case as demonstrated by several theoretical studies. We review the theoretical framework based on quantum electrodynamics, which has been shown to be necessary for an accurate description of time-resolved imaging of electron dynamics with ultrashort light pulses. We compare the results of theoretical studies of time-resolved nonresonant and resonant X-ray scattering, and time- and angle-resolved photoelectron spectroscopy and show that the corresponding time-resolved signals encode analogous information about electron dynamics. Thereby, the information about an electronic system provided by these time-resolved techniques is different from the information provided by their time-independent analogues.

We analyze the dynamics of fast electrons in plasmas containing partially ionized impurity atoms, where the screening effect of bound electrons must be included. We derive analytical expressions for the deflection and slowing-down frequencies, and show that they are increased significantly compared to the results obtained with complete screening, already at sub-relativistic electron energies. Furthermore, we show that the modifications to the deflection and slowing down frequencies are of equal importance in describing the runaway current evolution. Our results greatly affect fast-electron dynamics and have important implications, e.g. for the efficacy of mitigation strategies for runaway electrons in tokamak devices, and energy loss during relativistic breakdown in atmospheric discharges., Comment: 6 pages, 3 figures, fixed minor typos

Creation, erasing and ultrafast control of population density gratings using few-cycle optical pulses coherently interacting with resonant medium is discussed. In contrast to the commonly used schemes, here the pulses do not need to overlap in the medium, interaction between the pulses is mediated by excitation of polarization waves. We investigate the details of the dynamics arising in such ultrashort pulse scheme and develop an analytical theory demonstrating the importance of the phase memory effects in the dynamics.

International audience; In the presence of a (time-dependent) macroscopic electric field the electron dynamics of dielectrics cannot be described by the time-dependent density only. We present a real-time formalism that has the density and the macroscopic polarization P as key quantities. We show that a simple local function of P already captures long-range correlation in linear and nonlinear optical response functions. Specifically, after detailing the numerical implementation, we examine the optical absorption, the second-and third-harmonic generation of bulk Si, GaAs, AlAs and CdTe at different level of approximation. We highlight links with ultranonlocal exchange-correlation functional approximations proposed within linear response time-dependent density functional theory framework.

We investigated the ultrafast electron dynamics initiated by attosecond pulses in diatomic molecules and in a biomolecular building block, the amino acid phenylalanine, where a 30-fs charge migration process was measured.

Ultrafast transient reflectivity has been used to probe sub-picosecond electron dynamics in ultrathin gold films as a function of thickness and morphology. The data are discussed in terms of a modified two-temperature model. The implications of the results for controlling surface photochemistry through the substrate morphology are discussed.

The photochemistry of TiO2 has been studied intensively since it was discovered that TiO2 can act as a photocatalyst. Nevertheless, it has proven difficult to establish the detailed charge-transfer processes involved, partly because the excited states involved are difficult to study. Here we present evidence of the existence of hydroxyl-induced excited states in the conduction band region. Using two-photon photoemission, we show that stepwise photoexcitation from filled band gap states lying 0.8 eV below the Fermi level of rutile TiO2(110) excites hydroxyl-induced states 2.73 eV above the Fermi level that has an onset energy of ∼3.1 eV. The onset is shifted to lower energy by the coadsorption of molecular water, which suggests a means of tuning the energy of the excited state.

In hydrodynamic models of electron dynamics the additional boundary condition (ABC), required at the interface between a spatialy dispersive conductor and a local medium, is singled out by the set of ABCs imposed at the boundaries between non local conductors. We find the appropriate ABC at nonlocal-local conductor and nonlocal conductor-local insulator interfaces corresponding to several frequently used sets of ABCs.

Single‐particle motion of relativistic electrons in a cusped magnetic field has been studied both analytically and experimentally. The Lagrangian formulation is used to solve for the electron trajectories in some simple magnetic cusp configurations. A threshold energy for transmission through the cusp is found, and confirmed experimentally. Two different electron orbit off‐centering mechanisms are discussed; one arising from a nonzero radial component of particle velocity on the upstream side of the cusp transition, and another arising from the finite width of the cusp transition. Experiments are reported confirming the existence of these off‐centering mechanisms, and the results are compared with theoretical expectations.

The full electron dynamics in the collisionless drift wave radial equation is used to discover a class of drift modes which are localized by electron temperature gradients and are unaffected by the ion acoustic term. In the presence of a driving term, such as provided by trapped particles, these modes become strongly unstable.

The relation between several magnetic waves and instabilities is clarified. These modes involve only electron dynamics. It is shown that in the parameter regime of interest there are no propagating unstable waves driven by the first order baroclinic effect.

A theory of magnetically insulated flow is developed where two‐ or three‐dimensional spatial variation and temporal variation are allowed as long as the spatial variations in the flow direction are over many electron gyrolengths and temporal variations are over many electron gyroperiods. These criteria are met in most flows of interest. The theory is based upon describing the electron dynamics in terms of parameters which are constants of motion in one‐dimensional, time‐independent flows.

The wave particle cyclotron interaction is a basic process in collisionless plasmas, which results in the redistribution of the energy between plasma waves and charged particles. This paper present ...