Using Diffuse Scattering to Observe X-Ray-Driven Nonthermal Melting

NJ Hartley and J Grenzer and L Huang and Y Inubushi and N Kamimura and K Katagiri and R Kodama and A Kon and W Lu and M Makita and T Matsuoka and S Nakajima and N Ozaki and T Pikuz and AV Rode and D Sagae and AK Schuster and K Tono and K Voigt and J Vorberger and T Yabuuchi and EE McBride and D Kraus, PHYSICAL REVIEW LETTERS, 126, 015703 (2021).

DOI: 10.1103/PhysRevLett.126.015703

We present results from the SPring-8 Angstrom Compact free electron LAser facility, where we used a high intensity (similar to 10(20) W/cm(2)) x-ray pump x-ray probe scheme to observe changes in the ionic structure of silicon induced by x-ray heating of the electrons. By avoiding Laue spots in the scattering signal from a single crystalline sample, we observe a rapid rise in diffuse scattering and a transition to a disordered, liquidlike state with a structure significantly different from liquid silicon. The disordering occurs within 100 fs of irradiation, a timescale that agrees well with first principles simulations, and is faster than that predicted by purely inertial behavior, suggesting that both the phase change and disordered state reached are dominated by Coulomb forces. This method is capable of observing liquid scattering without masking signal from the ambient solid, allowing the liquid structure to be measured throughout and beyond the phase change.

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