# Evolution of coherent collective modes through consecutive CDW transitions in (PO$_{2}$)$_{4}$(WO$_{3}$)$_{12}$ mono-phosphate tungsten bronze

## TL;DR

This study investigates the evolution of collective modes through multiple charge density wave transitions in a tungsten bronze crystal using femtosecond optical spectroscopy, revealing mode interference effects and decoupling phenomena.

## Contribution

It provides the first detailed analysis of coherent collective modes across successive CDW transitions in this material using time-resolved spectroscopy and Ginzburg-Landau modeling.

## Key findings

- Observation of multiple transient coherent modes linked to each CDW transition
- Interference of modes causes an apparent rectification in reflectivity
- Mode amplitudes saturate below the CDW destruction threshold, indicating electronic-lattice decoupling

## Abstract

All optical femtosecond relaxation dynamics in a single crystal of mono-phosphate tungsten bronze (PO$_{2}$)$_{4}$(WO$_{3}$)$_{2m}$ with alternate stacking m=6 of WO$_{3}$ layers was studied through the three consequent charge density wave (CDW) transitions. Several transient coherent collective modes associated to the different CDW transitions were observed and analyzed in the framework of the time dependent Ginzburg-Landau theory. Remarkably, the interference of the modes leads to an apparent rectification effect in the transient reflectivity response. A saturation of the coherent-mode amplitudes with increasing pump fluence well below the CDWs destruction threshold fluence indicates a decoupling of the electronic and lattice parts of the order parameter under strong optical drive.