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 the use of advanced ultrafast probes sensitive to self-organised atomic-scale patterns. Here, we report the 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 × 3) superstructure of trimer clusters. Utilising MeV-scale ultrafast electron diffraction, we capture the photo-induced TaTe2 structural dynamics – exposing a rapid ≈ 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.

Accurate quantification of lattice temperature dynamics from ultrafast electron diffraction of single-crystal films using dynamical scattering simulations

“…This distribution can be considered as the convolution of the beam angular spread with the sample rippling such that the RMS tilt spread, , is given by is typically on the order of 1 mrad or less for transmission UED setups, 37 and depends on the sample preparation but can be as much as tens of mrad in some cases. 14 …”

“…In many UED experiments, RMS tilt spreads can be much smaller, especially if films are prepared on sturdy membrane supports, and deviations from the kinematical theory are more pronounced. 14 …”

“…Despite the reduced cross section for relativistic electron probes, such effects have still been observed in some experiments even at MeV-scale energies. 14 When these effects dominate, kinematical approximations are no longer valid, and modeling the complete “dynamical” diffraction process is required to match the diffraction signals.…”

Ultrafast Electron Diffraction: Visualizing Dynamic States of Matter

“…In some of its earliest manifestations, UED was used to probe strongly driven melting (order -disorder) transitions in materials, thanks to the ability of obtaining high quality diffraction patterns in a single shot. More recently, strongly-correlated or quantum materials have been the target of study (see for example (Kogar et al, 2020), (Duan et al, 2021) and (Siddiqui et al, 2021)). The non-equilibrium properties of quantum materials are particularly interesting because the interactions between lattice, charge, orbital or spin degrees of freedom are typically on par with electronic kinetic energy.…”

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 newly broken symmetry or topological phases, including charge density waves and metastable metallic states. − 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. In systems with antiferromagnetic order, magnon modes may emerge as collective excitations.…”