Dirk Gericke is a co-author on a paper published in Nature's free access journal "Scientific Reports"

Observation of inhibited electron-ion coupling in strongly heated graphite

T. G. White1, J. Vorberger2, C. R. D. Brown1,3, B. J. B. Crowley1,3, P. Davis4, S. H. Glenzer4, J.W.O. Harris3, D. C. Hochhaus5, S. Le Pape4, T. Ma4, C. D. Murphy1, P. Neumayer5, L. K. Pattison3, S. Richardson3, D. O. Gericke2 & G. Gregori1

1University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK, 2Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry, CV4 7AL, UK, 3AWE, Aldermaston, Reading, Berkshire, RG7 4PR, UK, 4Lawrence Livermore National Laboratory, PO Box 808, Livermore, CA 94551, USA, 5Extreme Matter Institute, GSI, Helmholtzzentrum fur Schwerionenforschung, Planckstr. 1, 64291 Darmstadt, Germany.

Creating non-equilibrium states of matter with highly unequal electron and lattice temperatures (Te ne Tion) allows unsurpassed insight into the dynamic coupling between electrons and ions through time-resolved energy relaxation measurements. Recent studies on low-temperature laser-heated graphite suggest acomplex energy exchange when compared to other materials. To avoid problems related to surface preparation, crystal quality and poor understanding of the energy deposition and transport mechanisms, we apply a different energy deposition mechanism, via laser-accelerated protons, to isochorically and non-radiatively heat macroscopic graphite samples up to temperatures close to the melting threshold. Using time-resolved x ray diffraction, we show clear evidence of a very small electron-ion energy transfer, yielding approximately three times longer relaxation times than previously reported. This is indicative of the existence of an energy transfer bottleneck in non-equilibrium warm dense matter.