# Stacking order dynamic in the quasi-two-dimensional dichalcogenide 1T-TaS$_2$ probed with MeV ultrafast electron diffraction

## TL;DR

This study uses MeV ultrafast electron diffraction to investigate how the stacking order of charge density waves in 1T-TaS$_2$ changes on ultrafast timescales, revealing phase transitions within a few picoseconds.

## Contribution

First-time measurement of out-of-plane stacking order dynamics in 1T-TaS$_2$ using ultrafast electron diffraction, showing rapid phase transitions between CDW states.

## Key findings

- The commensurate CDW phase disappears in 0.5 ps.
- The incommensurate CDW phase emerges in 2.0 ps.
- Results shed light on the metastable 'hidden' state in the material.

## Abstract

Transitions between different charge density wave (CDW) states in quasi-two-dimensional materials may be accompanied also by changes in the inter-layer stacking of the CDW. Using MeV ultrafast electron diffraction, the out-of-plane stacking order dynamics in the quasi-two-dimensional dichalcogenide 1T-TaS$_2$ is investigated for the first time. From the intensity of the CDW satellites aligned around the commensurate $l$ = 1/6 characteristic stacking order, it is found out that this phase disappears with a 0.5 ps time constant. Simultaneously, in the same experiment, the emergence of the incommensurate phase, with a slightly slower 2.0 ps time constant, is determined from the intensity of the CDW satellites aligned around the incommensurate $l$ = 1/3 characteristic stacking order. These results might be of relevance in understanding the metallic character of the laser-induced metastable "hidden" state recently discovered in this compound.

---
Source: https://tomesphere.com/paper/1703.05035