X-ray-induced fluidization: a non-equilibrium pathway to reach glasses at the extremes of their stability range.

I will address the fundamental question of what exactly are and how to prepare glasses at the extremes of their stability range: ultra-stable, ideal glasses on the one side and ultra-unstable, defect-saturated glasses on the opposite side. The ideal glass, predicted by some theories of the glass-transition but not yet observed, is a novel equilibrium state of matter characterized by a fairly unique, dense atomic structure with almost no defects. The defect-saturated glass is instead ductile, at odds with conventional glasses: any additional defect self-heals. I will reach these extraordinary states employing a non-thermal fluidization route activated by X-ray irradiation. Its non-equilibrium nature is key here: conventional thermal treatments, that induce structural changes stabilized by quenching, modify the properties of glasses only over a limited range. My project aims then at:1. producing ideal and defect-saturated glasses;2. developing a general scheme to control the stability of glasses;3. establishing experimentally the connection between their thermodynamic properties and their density of defects;4. clarifying the microscopic mechanism of X-ray induced fluidization;5. describing the glass-specificity of this effect in terms of amorphous plasticity.The importance of these extreme glasses is however not only fundamental: the reduced (zero?) density of defects makes the ideal glass mechanically and optically loss-free; a defect-saturated glass, instead, deforms under load and crystallizes very rapidly. Their properties are therefore enabling for new technological applications ranging from noise-free mechanical resonators, superconducting qubits with sufficient coherence for quantum computers and phase-change materials for applications as memories.The long-term vision is that the knowledge of how to measure and control the density of defects in glasses will lead to materials with extraordinary properties of relevance for many important applications.