Relaxation dynamics induced in glasses by absorption of hard x-ray photons

X-ray photon correlation is used to probe the slow dynamics of the glass-former B2O3 across the glass transition. In the undercooled liquid phase, the decay times of the measured correlation functions are consistent with visible light-scattering results and independent of the incoming flux; in the glass they are instead temperature independent and show a definite dependence on the x-ray flux since here the dynamics is artificially induced by the interaction with the x-ray beam. The decay times in this regime provide a measure of the number of atoms that rearrange on a length scale on the order of the inverse of the exchanged wave vector following an absorption event. Quite surprisingly, this number for the B2O3 glass is on the order of thousands of atoms. The induced dynamics persists also at higher temperatures until, close to the glass transition, it gets much slower than the intrinsic relaxation of the material. We suggest a possible scenario in which the single absorbed photon induces a collective motion of a volume of the glass with a size of the order of the nanometer.