The interaction of intense X-rays with glasses is traditionally regarded as a source of radiation damage that limits structural investigations. Over the past few years, however, it has become increasingly clear that X-ray irradiation can alternatively be viewed as a well-controlled external driving field capable of bringing amorphous materials in well-defined stationary states far from equilibrium. This perspective has led to the emergence of X-ray-driven glasses as a new class of driven disordered systems, opening unique opportunities to investigate non-equilibrium dynamics at the atomic scale.
In this contribution, I will review recent advances in the understanding of X-ray-driven glasses. I will first discuss how coherent X-ray scattering experiments revealed that X-ray irradiation induces an elastic-to-plastic crossover, establishing a close analogy with the yielding transition observed under mechanical loading. Coupling X-ray irradiation with flash calorimetry, I will also show that X-ray driven glasses are rejuvenated glasses but only to a limited extent, i.e. with a fictive temperature of the order of the mode-coupling critical temperature. I will then show how these findings have led to a broader framework in which irradiation-driven dynamics are interpreted in terms of the competition between defect creation, stress relaxation and structural evolution, providing a unified description of the stationary non-equilibrium state generated by irradiation.
These results establish X-ray irradiation as a clean, homogeneous and continuously tunable driving protocol, providing a unique experimental platform for exploring the microscopic physics of glasses driven far from equilibrium.