Electronic dispersion, correlations and stacking in the photoexcited state of 1T-TaS$_2$

TL;DR

This study uses advanced photoelectron spectroscopy to explore how photoexcitation affects electronic states, charge gaps, and correlations in 1T-TaS$_2$, revealing transient phases influenced by stacking and Coulomb screening.

Contribution

It provides new insights into the ultrafast dynamics of charge density waves and the role of stacking order and electronic correlations in 1T-TaS$_2$.

Findings

Photoexcitation erases band dispersion near the chemical potential.

Charge gap size is halved in the transient phase.

Stacking order influences Coulomb screening and electronic correlations.

Abstract

Here we perform angle and time-resolved photoelectron spectroscopy on the commensurate Charge Density Wave (CDW) phase of 1T-TaS$_2$. Data with different probe pulse polarization are employed to map the dispersion of electronic states below and above the chemical potential. Upon photoexcitation, the fluctuations of CDW order erase the band dispersion near to the chemical potential and halve the charge gap size. This transient phase sets within half a period of the coherent lattice motion and is favored by strong electronic correlations. The experimental results are compared to Density-Functional Theory (DFT) calculations with a self-consistent evaluation of the Coulomb repulsion. Our simulations indicate that the screening of Coulomb repulsion depends on the stacking order of the TaS$_2$ layers. The entanglement of such degrees of freedom suggest that both the structural order and electronic repulsion are locally modified by the photoinduced CDW fluctuations.