New Intercalant Order in TaS₂ Achieved by Pulsed Laser Heating

Transition metal dichalcogenides (TMDs) have attracted significant interest due to their rich electronic states and intriguing properties. Among TMDs, tantalum disulfide (TaS₂) stands out as an archetypical system, showcasing multiple superstructures contributed by charge density waves (CDW), such as sqrt(13x13) superstructures in 1T-TaS₂ and 3x3 in 2H-TaS₂ [1, 2]. In addition to the CDW, recent works have demonstrated another avenue for exotic superstructural harvest: the intentional doping through chemical intercalation within the van der Waals (vdW) gap, a process that also entails stoichiometric modification [3, 4].<br/><br/>Here, we discover a new 2x2 superstructure distinct from well-known chemically intercalated phases of TaS₂ with the assistance of pulsed laser heating. Employing <i>in situ</i> selected area electron diffraction (SAED) and atomic-resolution scanning transmission electron microscopy (STEM), we reveal the reversible order-disorder transition occurring at around ~483 K. Furthermore, we unveil a robust modulation of atomic density in real space, explicitly elucidating the origin of the 2x2 superstructure. Additionally, the local fluctuations in the chemical order at the nanoscale is observed. These results could pave the way to further refine the phase diagram of intercalated TaS₂ and provide insights into the atomic origin of the chemical ordering.<br/><br/>References:<br/><br/>1. J. A. Wilson, et al. Advances in Physics 24, 117 (1975)<br/>2. K. Rossnagel. Journal of Physics: Condensed Matter 23, 213001 (2021)<br/>3. X. Zhao, et al. Nature 581, 171-177 (2020)<br/>4. N. Agarwal, et al. Microscopy and Microanalysis 29, 1583-1584 (2023)