  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 the use of advanced ultrafast probes sensitive to self-organised
atomic-scale patterns. Here, we report the first ultrafast investigation of
TaTe2, which exhibits unique charge and lattice trimer order characterised by a
transition upon cooling from stripe-like chains into a $(3 \times 3)$
superstructure of trimer clusters. Utilising MeV-scale ultrafast electron
diffraction, we capture the photo-induced TaTe2 structural dynamics -- exposing
a rapid $\approx\!1.4$ ps melting of its low-temperature ordered state followed
by recovery via thermalisation into a hot cluster superstructure.
Density-functional calculations indicate that the initial quench is triggered
by intra-trimer Ta charge transfer which destabilises the clusters, unlike
melting of charge density waves in other TaX2 compounds. Our work paves the way
for further exploration and ultimately rapid optical and electronic
manipulation of trimer superstructures.
