Ultrafast optical melting of trimer superstructure in layered 1T'-TaTe2

Abstract

Quasi-two-dimensional transition metal dichalcogenides (TMDs) are a key platform for exploring emergent nanoscale phenomena arising from complex interactions. Access to the underlying degrees of freedom on their natural time scales motivates the use of advanced ultrafast probes that directly couple to the self-organised electronic and atomic structural order. Here, we report the first ultrafast investigation of TaTe 2 , which exhibits unique charge and lattice structural order characterised by a transition upon cooling from stripe-like trimer chains into a (3 × 3) superstructure of trimer clusters. Utilising MeV-scale ultrafast electron diffraction, the TaTe 2 structural dynamics is resolved following intense pulsed laser excitation at 1.2 eV. We observe a rapid ≈ 1.4 ps melting of the low-temperature ordered state, followed by recovery of the clusters via thermalisation into a hot superstructure persisting for extended times. Density-functional calculations indicate that the initial quench is triggered by Ta trimer bonding to nonbonding transitions that destabilises the clusters, unlike melting of charge density waves in other TaX 2 compounds. Our work paves the way for further exploration and ultimately directed manipulation of the trimer superstructure for novel applications.

INQ, a modern GPU-accelerated computational framework for (time-dependent) density functional theory

“…As an example application, two dimensional layered van der Waals systems with 5d heavy transition metals are a materials class where electron-electron interactions and the spin-orbit coupling are important energy scales. These materials are known to exhibit new broken symmetry or topological phases, including charge density waves and metastable metallic states [175][176][177][178][179]. Real-time TDDFT will clarify details of the mechanisms behind the evolution of charge instabilities, periodic lattice distortions, and coherent phonon generation in these 2D layered systems.…”