Crystallization as a local symmetry-breaking event in a tunable soft matter

Crystallization represents a pivotal local symmetry-breaking process that fundamentally shapes the structural and functional properties of material systems. Despite its importance, direct observation of its earliest stages remains elusive. Here, we introduce an in situ cryo-crystallization approach that captures the nucleation dynamics within a tunable soft-matter field composed of oxometalate assemblies. Employing a dimethyl sulfoxide (DMSO)-water glass matrix, we finely control the solvent environment to suppress background noise and inhibit mechanical fracture, thereby enabling unprecedented visualization of symmetry breaking at the onset of crystallization. This method reveals the formation of ordered oxometalate domains that precede the crystallization of {Mo 7 } clusters, offering rare insights into pre-nucleation ordering. Our findings establish a framework for interpreting crystallization as a symmetry-breaking process and provide a new strategy to engineer material architectures through controlled phase evolution.