Ultrafast dynamics of charge density waves in 4H(b)-TaSe2 probed by femtosecond electron diffraction

Phys Rev Lett. 2012 Oct 19;109(16):167402. doi: 10.1103/PhysRevLett.109.167402. Epub 2012 Oct 18.


The dynamics of the photoinduced commensurate-to-incommensurate charge density wave (CDW) phase transition in 4H(b)-TaSe(2) are investigated by femtosecond electron diffraction. In the perturbative regime, the CDW re-forms on a 150-ps time scale, 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.