Ken R. Ferguson 1 , 2 , Maximilian Bucher 1 , Tais Gorkhover 1 , 3 , Sébastien Boutet 1 , Hironobu Fukuzawa 4 , Jason E. Koglin 1 , Yoshiaki Kumagai 4 , Alberto Lutman 1 , Agostino Marinelli 1 , Marc Messerschmidt 5 , Kiyonobu Nagaya 6 , Jim Turner 1 , Kiyoshi Ueda 4 , Garth J. Williams 1 , Philip H. Bucksbaum 2 , 7 , Christoph Bostedt 1 , 7 , 8 , 9 , *
29 January 2016
Ultrafast x-ray heating of clusters leads to bond contraction in the solid-to-plasma transition.
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.