The description of the electronic structure of molecules in terms of molecular orbitals is a highly successful concept in chemistry. However, it commonly fails if the electrons in a molecule are ...strongly correlated and cannot be treated as independent particles. Electron correlation is essential to understand inner‐valence X‐ray spectroscopies, it can drive ultrafast charge migration in molecules, and it is responsible for many exotic properties of strongly correlated materials. Time‐resolved spectroscopy with attosecond resolution is generally capable of following electronic motion in real time and can thus provide experimental access to electron‐correlation‐driven phenomena. High‐harmonic spectroscopy in particular uses the precisely timed laser‐driven recollision of electrons to interrogate the electronic structure and dynamics of the investigated system on a sub‐femtosecond timescale. In this Review, the capabilities of high‐harmonic spectroscopy to follow electronic motion in molecules are discussed. Both qualitative and quantitative approaches to unraveling the detailed dynamical responses of molecular systems following ionization are presented. A new theoretical formalism for the reconstruction of correlation‐driven charge migration is introduced. The importance of electron–ion entanglement and electronic coherence in the reconstruction of attosecond hole dynamics are discussed. These advances make high‐harmonic spectroscopy a promising technique to decode fundamental electron correlations and to provide experimental data on the complex manifestations of multi‐electron dynamics.
The concept of molecular orbitals, one of the most successful in chemistry, commonly fails if strong electron correlation is present. This Review shows how high‐harmonic generation, the process for generating attosecond pulses in the extreme ultraviolet, can be used to spectroscopically access electron dynamics in molecules following ionization, and how the technique could be extended to identify the effects of electron correlation on dynamics.
Understanding excited carrier dynamics in semiconductors is crucial for the development of photovoltaics and efficient photonic devices. However, overlapping spectral features in optical pump-probe ...spectroscopy often render assignments of separate electron and hole carrier dynamics ambiguous. Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin films are directly and simultaneously observed by ultrafast transient absorption spectroscopy in the extreme ultraviolet at the germanium M
edge. We decompose the spectra into contributions of electronic state blocking and photo-induced band shifts at a carrier density of 8 × 10
cm
. Separate electron and hole relaxation times are observed as a function of hot carrier energies. A first-order electron and hole decay of ∼1 ps suggests a Shockley-Read-Hall recombination mechanism. The simultaneous observation of electrons and holes with extreme ultraviolet transient absorption spectroscopy paves the way for investigating few- to sub-femtosecond dynamics of both holes and electrons in complex semiconductor materials and across junctions.
PurposeIn a move characterized by ambiguity, Facebook changed its name to Meta in October 2021, announcing a new era of social interaction, enabled by the metaverse technology that appears poised to ...become the future center of gravity for online social interactions. At first glance, the communicated change signals a radically new business model (BM) based on an unprecedented configuration of the three following components: value creation, value proposition and value capture. The purpose of this paper is to analyze Facebook’s announced changes in its BM to clarify whether the change is as radical as communicated or rather represents an incremental transformation of the current BM.Design/methodology/approachThis investigation adopted an in-depth case study research method. The process included using a structured approach to collect 153 data points, including academic studies and publicly available information, followed by qualitative content analysis.FindingsThe results of our analysis of Facebook’s entrepreneurial journey indicate that the communicated strategic refocusing does not correspond to a radical BM innovation pattern. Even though Facebook’s BM might evolve into the innovation phase, as the current changes appear very futuristic, the authors estimate that the core elements of the BM will change incrementally. The investigation indicates that the underlying logic of the straightforward communicative efforts primarily serves two purposes: to improve the external perception of the company and to disseminate an internal change signal within the organization.Originality/valueThis paper is the first study that takes an entrepreneurship and BM perspective in analyzing Facebook’s approach in rebranding to Meta and refocusing its strategy on building the metaverse. The academic and practical relevance, as well as the potential future impact on business and society, makes the investigation of this case an intriguing prospect. Additionally, the study illuminates the difference between the communicated vision and the real impact on the business, suggesting critical questions about future large-scale rebranding efforts and their effects.
Attaining competitive advantage is especially crucial for innovative firms. Due to increased competition, firms employ various types of innovation activities to position themselves against their ...competitors. Ambidexterity and strategic agility have been found to strengthen this position. Whereas scholars analyzed strategic agility's and ambidexterity's impact on organizational performance, ambidexterity's impact on the competitive advantage of organizations remains largely unexplored. Tensions between exploration and exploitation within an ambidextrous strategy make it difficult to reap benefits in establishing competitive advantage. Contrary, strategic agility centers on organization's capacities to quickly respond to shifting demand, hence, increasing its competitive advantage. Through a mixed-method approach, comprising of a literature review and quantitative analyses of 150 German mid-sized firms in the engineering industry, it is demonstrated how ambidexterity, exploration and exploitation, in conjunction with strategic agility, affect the competitive advantage of firms. In order to sustain, firms should either favor an exploration strategy of innovation processes to come up with radically new knowledge, products and services, or combine an exploitation strategy with strategic agility. A strategy of sole exploitation is not beneficial towards increased competitive advantage, while an ambidextrous strategy seems to even negatively influence the competitive advantage of a firm.
We present a table-top beamline providing a soft X-ray supercontinuum extending up to 370 eV from high-order harmonic generation with sub-13 fs 1300 nm driving pulses and simultaneous production of ...sub-5 fs pulses centered at 800 nm. Optimization of high harmonic generation in a long and dense gas medium yields a photon flux of ~ 1.4 × 10
photons/s/1% bandwidth at 300 eV. The temporal resolution of X-ray transient absorption experiments with this beamline is measured to be 11 fs for 800 nm excitation. This dual-wavelength approach, combined with high flux and high spectral and temporal resolution soft X-ray absorption spectroscopy, is a new route to the study of ultrafast electronic dynamics in carbon-containing molecules and materials at the carbon K-edge.
Coulomb correlations can manifest in exotic properties in solids, but how these properties can be accessed and ultimately manipulated in real time is not well understood. The insulator-to-metal phase ...transition in vanadium dioxide (VO₂) is a canonical example of such correlations. Here, few-femtosecond extreme UV transient absorption spectroscopy (FXTAS) at the vanadium M
2,3 edge is used to track the insulator-to-metal phase transition in VO₂. This technique allows observation of the bulk material in real time, follows the photoexcitation process in both the insulating and metallic phases, probes the subsequent relaxation in the metallic phase, and measures the phase-transition dynamics in the insulating phase. An understanding of the VO₂ absorption spectrum in the extreme UV is developed using atomic cluster model calculations, revealing V3+/d² character of the vanadium center. We find that the insulator-to-metal phase transition occurs on a timescale of 26 ± 6 fs and leaves the system in a long-lived excited state of the metallic phase, driven by a change in orbital occupation. Potential interpretations based on electronic screening effects and lattice dynamics are discussed. A Mott–Hubbard-type mechanism is favored, as the observed timescales and d² nature of the vanadium metal centers are inconsistent with a Peierls driving force. The findings provide a combined experimental and theoretical roadmap for using time-resolved extreme UV spectroscopy to investigate nonequilibrium dynamics in strongly correlated materials.
Improving the brightness of high-harmonic generation (HHG) sources is one of the major goals for next-generation ultrafast, imaging and metrology applications in the extreme-ultraviolet spectrum. ...Previous research efforts have demonstrated a plethora of techniques to increase the conversion efficiency of HHG. However, few studies so far have addressed how to simultaneously minimize the divergence and improve focusability, which all contribute to an increased brightness of the source. Here, we investigate how to improve both photon yield and divergence, which is directly linked to focusability, when adding the second harmonic to the fundamental driving field. We study the effects of the relative polarization in two-color HHG and compare the results to a one-color configuration. In a perpendicular two-color field, the relative phase between the two colors can be used to suppress or enhance recombination of either the long or the short trajectories. This allows to exert control over the divergence of the harmonics. In a parallel two-color field, the ionization rate is modified through the two-color phase, which selects trajectories during the ionization step. This enhances the total yield. We elaborate on the underlying mechanisms for parallel, perpendicular, and intermediate polarization angles, and confirm our experimental observations with simulations.
The transfer of charge at the molecular level plays a fundamental role in many areas of chemistry, physics, biology and materials science. Today, more than 60 years after the seminal work of R. A. ...Marcus, charge transfer is still a very active field of research. An important recent impetus comes from the ability to resolve ever faster temporal events, down to the attosecond time scale. Such a high temporal resolution now offers the possibility to unravel the most elementary quantum dynamics of both electrons and nuclei that participate in the complex process of charge transfer. This review covers recent research that addresses the following questions. Can we reconstruct the migration of charge across a molecule on the atomic length and electronic time scales? Can we use strong laser fields to control charge migration? Can we temporally resolve and understand intramolecular charge transfer in dissociative ionization of small molecules, in transition-metal complexes and in conjugated polymers? Can we tailor molecular systems towards specific charge-transfer processes? What are the time scales of the elementary steps of charge transfer in liquids and nanoparticles? Important new insights into each of these topics, obtained from state-of-the-art ultrafast spectroscopy and/or theoretical methods, are summarized in this review.
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