Domain-size effects on the dynamics of a charge density wave in 1T−TaS2

Abstract

Recent experiments have shown that the high temperature incommensurate (I) charge density wave (CDW) phase of 1T-TaS2 can be photoinduced from the lower temperature, nearly commensurate (NC) CDW state. Here we report a time-resolved x-ray diffraction study of the growth process of the photoinduced I-CDW domains. The layered nature of the material results in a marked anisotropy in the size of the photoinduced domains of the I-phase. These are found to grow self-similarly, their shape remaining unchanged throughout the growth process. The photoinduced dynamics of the newly formed I-CDW phase was probed at various stages of the growth process using a double pump scheme, where a first pump creates I-CDW domains and a second pump excites the newly formed I-CDW state. We observe larger magnitudes of the coherently excited I-CDW amplitude mode in smaller domains, which suggests that the incommensurate lattice distortion is less stable for smaller domain sizes.

Intertwined chiral charge orders and topological stabilization of the light-induced state of a prototypical transition metal dichalcogenide

“…34 Recent experiments on the IC to NC transition show that the domain structure continues to grow on a timescale up to~100 ps. 14,15,17,47 The final result is the rotation of the transient ordering vector 31 towards Q H and the mismatch between the new H order and C order is revealed in the longrange Moiré pattern. Local changes in the domains' structure and size or LRO can be seen in the opt-H state on longer timescales (e.g.…”

“…The problem is that the lifetimes of the transient states, usually ranging from picoseconds to microseconds, [2][3][4][5]7 limit the methods that are available, 11,12 making non-periodic mesoscopic orders and microscopic features experimentally inaccessible by even the most advanced techniques. 10,[13][14][15][16][17] Uniquely, the transition metal dichalcogenide 1T-TaS 2 (TDS) has a metastable light-induced state with a temperature-tunable lifetime, which is usefully long at low temperatures. 6,18 This opens the possibility to investigate its emergent ordering and origins of metastability on multiple length scales and with great detail with the aid of scanning tunneling microscopy (STM).…”

“…The various states can be accessed by varying the temperature, 19 pressure 20,21 or doping. 22 The NC-IC non-equilibrium transition was investigated recently by electron diffraction 13,17 and X-ray diffraction methods 14,15 revealing relaxation dynamics on a 100 ps timescale that was interpreted to arise from domain formation and growth. However, domains were so far not directly observed, and their structure or hypothetical ordering was not reported.…”

Incommensurate charge-density-waves as seen by time-resolved x-ray diffraction

“…In the blue bronze, the melting of the incommensurate phase, which is second order, is driven by a coherent phonon: the amplitude mode of the incommensurate state. In the IT-TaS2 case, where the transition is first order, we give evidence that the photo-induced incommensurate phase develops by a fast sub-ns nucleation-growth-coarsening process never observed before [3][4].…”

“…In this work, we compare the dynamical behavior of CDW after an infrared laser pulse in three different incommensurate DW systems: Chromium [1], K0.3MoO3 (so-called blue bronze) [2], and 1T-TaS2 [3][4]. We use pump-probe diffraction techniques to follow the incommensurate reflections (position, width and intensity) as a function of the delay between the infrared pulse and the X-ray pulse.…”