Topological defects determine evolution of charge density wave phase transition

Quantum materials exhibit exotic properties and can exhibit new functionality and applications when brought out of equilibrium and changing their properties. Such transient states are inherently inhomogeneous, characterized by the formation of topologically protected structures, requiring nanometer spatial resolution on femtosecond timescales to resolve their evolution. 

Total x-ray scattering signals of the charge density wave material LaTe₃ were measured after ultrafast laser excitation at Bernina/SwissFEL. A sophisticated scaling analysis of the diffuse scattering signals provides new insights into the dynamics on the required mesoscopic length scale. The results show direct evidence for topological vortex strings of the charge density wave, formed after ultrafast laser excitation out of equilibrium. The following re-equilibration of these topological defects is dominated by anomalous, subdiffusive dynamics, which slows down the process.

The findings establish a novel general framework to investigate properties of topological defects, which occur in non-equilibrium phase transitions.  As they can hinder equilibration processes they enhance the coexistence of competing ordering phenomena with very different properties.