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Transient lattice contraction in the solid-to-plasma transition

Ferguson, K. R.; Bucher, M.; Gorkhover, Tais; Boutet, S.; Fukuzawa, H.; Koglin, J. E.; Kumagai, Y.; Lutman, A.; Marinelli, A.; Messerschmidt, M.; Nagaya, K.; Turner, J.; Ueda, K.; Williams, G. J.; Bucksbaum, P. H.; Bostedt, C.

FG Energietechnik und Umweltschutz

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.