Unexpected interplay of CDW and screened Coulomb repulsion

Within an international collaboration, our group explored the commensurate charge density wave (CDW) phase of 1T-TaS₂ by means of angle and time-resolved photoelectron spectroscopy.  The approach of this compelling study included varying probe pulse polarizations to map electronic state dispersion both above and below the chemical potential. Intriguingly, upon photoexcitation, the CDW order fluctuations exhibited a remarkable ability to erase band dispersion and compress electronic states near the chemical potential. This transient phenomenon emerged swiftly, aligning with half a period of the coherent lattice motion and was notably influenced by strong electronic correlations.

To gain deeper insights, density-functional theory calculations with a self-consistent evaluation of Coulomb repulsion were performed. These simulations revealed that the screening of Coulomb repulsion hinged on the stacking order of TaS₂ layers. The intricate interplay of these degrees of freedom suggested that both structural order and electronic repulsion were locally modified by the photoinduced CDW fluctuations. Ultimately, this study provided valuable revelations about the C-CDW phase of 1T-TaS2, depicting it as an insulator entangled with out-of-plane dimerization and intricate electronic correlations. The research underscored how photoinduced fluctuations can disrupt long-range order, presenting a compelling avenue for further exploration in the ultrafast phase transition domain.

Original publication: 
Electronic dispersion, correlations and stacking in the photoexcited state of 1T-TaS₂
Jingwei Dong et al., 2D Mater. 10,  045001 (2023)