Watching atoms move: an ultrafast phase transition

One approach to advance our understanding of the complex interactions between different degrees of freedom in strongly correlated systems is to use time-resolved methods to study the response of a material after it has been driven out of equilibrium. Ultrafast optical techniques have demonstrated considerable potential to unravel the correlations that drive the interesting physics in such materials. Phonon dynamics in these studies are only indirectly observed via the electronic response, and are not generally able to unambiguously disentangle the dynamics of the lattice from those of the electronic subsystem. By using femtosecond x-ray diffraction to probe directly the structural response of photoexcited manganite, we have found evidence of an ultrafast laser-induced structural phase transition driven directly by electronic excitation and occuring on a sub-picosecond time scale.

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