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      Transient lattice contraction in the solid-to-plasma transition

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          Abstract

          Ultrafast x-ray heating of clusters leads to bond contraction in the solid-to-plasma transition.

          Abstract

          In condensed matter systems, strong optical excitations can induce phonon-driven processes that alter their mechanical properties. We report on a new phenomenon where a massive electronic excitation induces a collective change in the bond character that leads to transient lattice contraction. Single large van der Waals clusters were isochorically heated to a nanoplasma state with an intense 10-fs x-ray (pump) pulse. The structural evolution of the nanoplasma was probed with a second intense x-ray (probe) pulse, showing systematic contraction stemming from electron delocalization during the solid-to-plasma transition. These findings are relevant for any material in extreme conditions ranging from the time evolution of warm or hot dense matter to ultrafast imaging with intense x-ray pulses or, more generally, any situation that involves a condensed matter-to-plasma transition.

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          Most cited references 16

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          An atomic-level view of melting using femtosecond electron diffraction.

          We used 600-femtosecond electron pulses to study the structural evolution of aluminum as it underwent an ultrafast laser-induced solid-liquid phase transition. Real-time observations showed the loss of long-range order that was present in the crystalline phase and the emergence of the liquid structure where only short-range atomic correlations were present; this transition occurred in 3.5 picoseconds for thin-film aluminum with an excitation fluence of 70 millijoules per square centimeter. The sensitivity and time resolution were sufficient to capture the time-dependent pair correlation function as the system evolved from the solid to the liquid state. These observations provide an atomic-level description of the melting process, in which the dynamics are best understood as a thermal phase transition under strongly driven conditions.
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            Non-thermal melting in semiconductors measured at femtosecond resolution.

            Ultrafast time-resolved optical spectroscopy has revealed new classes of physical, chemical and biological reactions, in which directed, deterministic motions of atoms have a key role. This contrasts with the random, diffusive motion of atoms across activation barriers that typically determines kinetic rates on slower timescales. An example of these new processes is the ultrafast melting of semiconductors, which is believed to arise from a strong modification of the inter-atomic forces owing to laser-induced promotion of a large fraction (10% or more) of the valence electrons to the conduction band. The atoms immediately begin to move and rapidly gain sufficient kinetic energy to induce melting--much faster than the several picoseconds required to convert the electronic energy into thermal motions. Here we present measurements of the characteristic melting time of InSb with a recently developed technique of ultrafast time-resolved X-ray diffraction that, in contrast to optical spectroscopy, provides a direct probe of the changing atomic structure. The data establish unambiguously a loss of long-range order up to 900 A inside the crystal, with time constants as short as 350 femtoseconds. This ability to obtain the quantitative structural characterization of non-thermal processes should find widespread application in the study of ultrafast dynamics in other physical, chemical and biological systems.
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              Detection of nonthermal melting by ultrafast X-ray diffraction.

              Using ultrafast, time-resolved, 1.54 angstrom x-ray diffraction, thermal and ultrafast nonthermal melting of germanium, involving passage through nonequilibrium extreme states of matter, was observed. Such ultrafast, optical-pump, x-ray diffraction probe measurements provide a way to study many other transient processes in physics, chemistry, and biology, including direct observation of the atomic motion by which many solid-state processes and chemical and biochemical reactions take place.
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                Author and article information

                Journal
                Sci Adv
                Sci Adv
                SciAdv
                advances
                Science Advances
                American Association for the Advancement of Science
                2375-2548
                January 2016
                29 January 2016
                : 2
                : 1
                Affiliations
                [1 ]Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
                [2 ]Department of Applied Physics, Stanford University, Stanford, CA 94305, USA.
                [3 ]Institut für Optik und Atomare Physik, Technische Universität Berlin, 10623 Berlin, Germany.
                [4 ]Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan.
                [5 ]National Science Foundation BioXFEL Science and Technology Center, Buffalo, NY 14203, USA.
                [6 ]Division of Physics and Astronomy, Kyoto University, Kyoto 606-8501, Japan.
                [7 ]Pulse Institute, Stanford University and SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
                [8 ]Argonne National Laboratory, Lemont, IL 60439, USA.
                [9 ]Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA.
                Author notes
                [* ]Corresponding author. E-mail: cbostedt@ 123456anl.gov
                Article
                1500837
                10.1126/sciadv.1500837
                4846449
                27152323
                Copyright © 2016, The Authors

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited.

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                Research Article
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                Nanostructures
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                Mau Buenaventura

                scattering, ultrafast, cluster, x-ray

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