PT - JOURNAL ARTICLE AU - Ferguson, Ken R. AU - Bucher, Maximilian AU - Gorkhover, Tais AU - Boutet, Sébastien AU - Fukuzawa, Hironobu AU - Koglin, Jason E. AU - Kumagai, Yoshiaki AU - Lutman, Alberto AU - Marinelli, Agostino AU - Messerschmidt, Marc AU - Nagaya, Kiyonobu AU - Turner, Jim AU - Ueda, Kiyoshi AU - Williams, Garth J. AU - Bucksbaum, Philip H. AU - Bostedt, Christoph TI - Transient lattice contraction in the solid-to-plasma transition AID - 10.1126/sciadv.1500837 DP - 2016 Jan 01 TA - Science Advances PG - e1500837 VI - 2 IP - 1 4099 - http://advances.sciencemag.org/content/2/1/e1500837.short 4100 - http://advances.sciencemag.org/content/2/1/e1500837.full SO - Sci Adv2016 Jan 01; 2 AB - 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.