Ultrafast optical melting of trimer superstructure in layered 1T?-TaTe2

Abstract Quasi-two-dimensional transition-metal dichalcogenides 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 use of advanced ultrafast probes sensitive self-organised atomic-scale patterns. Here, we report investigation TaTe 2 , which exhibits unique charge and lattice trimer order characterised by transition upon cooling stripe-like chains into (3 × 3) superstructure clusters. Utilising MeV-scale electron diffraction, capture photo-induced structural dynamics – exposing rapid ? 1.4 ps melting its low-temperature ordered state followed recovery via thermalisation hot cluster superstructure. Density-functional calculations indicate that initial quench is triggered intra-trimer Ta transfer destabilises clusters, unlike density waves in other TaX compounds. Our work paves way further exploration ultimately optical electronic manipulation superstructures.