Attosecond core-level spectroscopy reveals the flow of excitation in a material between light, carriers and phonons

© 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.We use attosecond core-level X-ray spectroscopy to disentangle the spectral and dynamical signatures of energy conversion pathways between photons, charge carriers and the lattice in graphite with attosecond precision and across a picosecond range.Peer ReviewedArticle signat per 19 autors/es: T.P.H. Sidiropoulos1*, N. Di Palo1, D.E. Rivas1,2, S. Severino1, M. Reduzzi1, B. Nandy1, B. Bauerhenne3, S. Krylow3, T. Vasileiadis4, T. Danz5, P. Elliott6,7, S. Sharma6, K. Dewhurst7, C. Ropers5, Y. Joly8, K. M. E. Garcia3, M. Wolf4, R. Ernstorfer4, J. Biegert1,9 // 1 ICFO - Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain; 2 European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Germany; 3 Theoretische Physik, FB-10, Universität Kassel, 34132 Kassel, Germany; 4 Fritz Haber Institute of the Max Planck Society, Berlin, Germany; 5 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Germany; 6 Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, 12489 Berlin, Germany; 7 Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany; 8 Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France; 9 ICREA - Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain // * present address: Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, 12489 Berlin, GermanyPostprint (author's final draft

Performance of state-of-the-art force fields for atomistic simulations of silicon at high electronic temperatures

Intensive femtosecond laser pulses or ion bombardment drives Silicon (Si) into a nonequilibrium state with hot electrons and cold ions. Since ab initio molecular dynamics (MD) simulations can only deal with at most 103 atoms, an analytical interatomic potential (or force field) is necessary for performing large-scale simulations describing Si in nonequilibrium. We recently constructed a potential for Si at high electronic temperatures Te’s, which was developed from ab initio MD simulations. In this study, we analyze the performance of this potential compared to other available Te-dependent Si potentials and to some widely used ground state Si potentials, which were adapted to nonequilibrium by fitting their parameters to ab initio MD simulations. We analyze the ability for reproducing nonthermal effects like thermal phonon squeezing and ultrafast melting in bulk Si as well as the expansion due to bond softening of a thin Si film. Our results show that the available Te-dependent potentials cannot quantitatively describe the latter. A much better description is given by the potentials with parameters fitted to ab initio MD simulations. Our proposed potential gives the best description among the studied ones, since its analytical shape was optimized for the ground and the laser excited state

Neural network interatomic potential for laser-excited materials

Abstract Data-driven interatomic potentials based on machine-learning approaches have been increasingly used to perform large-scale, first-principles quality simulations of materials in the electronic ground state. However, they are not able to describe situations in which the electrons are excited, like in the case of material processing by means of femtosecond laser irradiation or ion bombardment. In this work, we propose a neural network interatomic potential with an explicit dependency on the electronic temperature. Taking silicon as an example, we demonstrate its capability of reproducing important physical properties with first-principles accuracy and use it to simulate laser-induced surface modifications on a thin film at time and length scales that are impossible to reach with first-principles approaches like density functional theory. The method is general and can be applied not only to other laser-excited materials but also to condensed and liquid matter under non-equilibrium situations in which electrons and ions exhibit different temperatures

Neural network interatomic potential for laser-excited materials

Gefördert im Rahmen des Projekts DEA

Biomolecular structure manipulation using tailored electromagnetic radiation

We report on the viability of breaking selected bonds in biological systems using tailored electromagnetic radiation.</p