Tracking the ultrafast XUV optical properties of x-ray free-electron-laser heated matter with high-order harmonics

Williams, G.; Künzel, S.; Daboussi, S.; Iwan, Bianca; Gonzalez, A. I.; Boutu, Willem; Hilbert, V.; Zastrau, U.; Lee, H. J.; Nagler, Bob; Galtier, E.; Heimann, Philip; Barbrel, B.; Dovillaire, Guillaume; Lee, R. W.; Dunn, James P.; Recoules, V.; Blancard, C.; Renaudin, P.; Varga, Alberto G. de la; Velarde, P.; Audebert, P.; Merdji, H.; Zeitoun, Ph.; Fajardo, M.

doi:10.1103/physreva.97.023414

Cited by 19 publications

(31 citation statements)

References 57 publications

(91 reference statements)

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“…This approximation is based on efficient screening of the optical field by surface electrons 21 and space-charge limitation of the maximum optical field intensity 22 . In contrast, femto-and picosecond core-level photoabsorption of metals systematically shows signatures of excitation-induced electronic structure modification at high intensities [23][24][25][26] . To bridge this gap of intensities and timescales, we used attosecond transient absorption spectroscopy to study collective electron dynamics in the transition metals Ti and Zr.…”

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confidence: 92%

Attosecond screening dynamics mediated by electron localization in transition metals

et al. 2019

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Transition metals with their densely confined and strongly coupled valence electrons are key constituents of many materials with unconventional properties 1 , such as high-Tc superconductors, Mott insulators and transition-metal dichalcogenides 2 . Strong electron interaction offers a fast and efficient lever to manipulate their properties with light, creating promising potential for next-generation electronics 3-6 . However, the underlying dynamics is a fast and intricate interplay of polarization and screening effects, which is poorly understood. It is hidden below the femtosecond timescale of electronic thermalization, which follows the light-induced excitation 7 . Here, we investigate the many-body electron dynamics in transition metals before thermalization sets in. We combine the sensitivity of intra-shell transitions to screening effects 8 with attosecond time resolution to uncover the interplay of photo-absorption and screening. First-principles time-dependent calculations allow us to assign our experimental observations to ultrafast electronic localization on d-orbitals. The latter modifies the whole electronic structure as well as the collective dynamic response of the system on a timescale much faster than the light-field cycle. Our results demonstrate a possibility for steering the electronic properties of solids prior to electron thermalization, suggesting that the ultimate speed of electronic phase transitions is limited only by the duration of the controlling laser pulse. Furthermore, external control of the local electronic density serves as a fine tool for testing state-of-the art models of electron-electron interactions. We anticipate our study to facilitate further investigations of electronic phase transitions, laser-metal interactions and photo-absorption in correlated electron systems on its natural timescale.A characteristic thermalization time of laser-excited hot electrons in solids is in the femtosecond regime and becomes faster with stronger electron interactions 7 . Therefore, attosecond time resolution is required to resolve coupled electron dynamics during the lasermatter interaction before electron thermalization has occurred. Attosecond transient absorption spectroscopy revealed electric-field-guided electron dynamics in simple dielectrics and semiconductors 9-14 . However, transient absorption studies of localized and strongly interacting electrons, such as on d-and f-orbitals of transition metals, have been limited to the fewfemtosecond regime 15 . Transition metal elements are the key constituents of many materials exhibiting remarkable properties, such as Mott insulators, high-Tc superconductors and transition metal dichalcogenides 2 . Understanding the coupled-electron dynamics in these systems is central for their applications in optoelectronics, energy-efficient electronics, magnetic-memory devices, spintronics and new solar cells 16 . Transition metal elements were studied with attosecond photoemission spectroscopy [17][18][19] . However, state-of-the-art theoretical

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confidence: 92%

Attosecond screening dynamics mediated by electron localization in transition metals

et al. 2019

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“…Because of its convenient electronic structure and the near-free behavior of its valence electrons, aluminum irradiated at extreme ultraviolet (XUV) wavelengths is an ideal test bed to study free-free light-matter interactions at high electron densities. In this context, recent attempts have been made aimed at understanding historical discrepancies in the predicted and measured absorption coefficients in ground state Al at XUV wavelengths [10], with further investigations pushing well into the warm dense matter regime [11,12]. Current theoretical predictions generally agree that the free-free absorption cross section should initially increase as the temperature of the system is raised to the Fermi temperature [10,[13][14][15], before starting to fall off at higher temperatures according to the T −3=2 temperature dependence of inverse bremsstrahlung (IB) theory [16].…”

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confidence: 99%

Time-Resolved XUV Opacity Measurements of Warm Dense Aluminum

et al. 2020

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“…Dense plasmas, in turn, have proven far more challenging both to model and to investigate experimentally [9][10][11][12][13][14]. Perhaps surprisingly, similar difficulties are encountered in condensed matter systems such as ground-state and liquid metals.…”

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confidence: 99%

Ab initio simulations and measurements of the free-free opacity in aluminum

et al. 2019

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The free-free opacity in dense systems is a property that both tests our fundamental understanding of correlated many-body systems, and is needed to understand the radiative properties of high energy-density plasmas. Despite its importance, predictive calculations of the free-free opacity remain challenging even in the condensed matter phase for simple metals. Here we show how the freefree opacity can be modelled at finite-temperatures via time-dependent density functional theory, and illustrate the importance of including local field corrections, core polarization and self-energy corrections. Our calculations for ground-state Al are shown to agree well with experimental opacity measurements performed on the Artemis laser facility across a wide range of x-ray to ultraviolet wavelengths. We extend our calculations across the melt to the warm-dense matter regime, and find good agreement with advanced plasma models based on inverse bremsstrahlung at temperatures above 10 eV.

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Tracking the ultrafast XUV optical properties of x-ray free-electron-laser heated matter with high-order harmonics

Cited by 19 publications

References 57 publications

Attosecond screening dynamics mediated by electron localization in transition metals

Attosecond screening dynamics mediated by electron localization in transition metals

Time-Resolved XUV Opacity Measurements of Warm Dense Aluminum

Ab initio simulations and measurements of the free-free opacity in aluminum

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