Ultrafast dynamics of charge density waves in 4Hb-TaSe2 probed by femtosecond electron diffraction

TL;DR

This study investigates the ultrafast dynamics of charge density waves in 4Hb-TaSe2 using femtosecond electron diffraction, revealing slow reformation times and the influence of three-dimensionality on phase transition behavior.

Contribution

It demonstrates the slow reformation of CDWs in 4Hb-TaSe2 and highlights the role of three-dimensionality in CDW dynamics, with insights into phase transition order.

Findings

CDW reforms in 150 ps, much slower than in other materials.

Weak coupling between T-layers affects CDW dynamics.

Optical excitation induces a second order phase transition.

Abstract

The dynamics of the photoinduced commensurate to incommensurate charge density wave (CDW) phase transition in 4Hb-TaSe2 are investigated by femtosecond electron diffraction. In the perturbative regime the CDW reforms on a 150 ps timescale, which is two orders of magnitude slower than in other transition-metal dichalcogenides. We attribute this to a weak coupling between the CDW carrying T-layers and thus demonstrate the importance of three-dimensionality for the existence of CDWs. With increasing optical excitation the phase transition is achieved showing a second order character in contrast to the first order behavior in thermal equilibrium.