Reconstructed Electronic Structure in 2D vdW 1T-Ta$S_2$ for Quantum Sensing and Information Science

Abstract

Transition metal dichalcogenides (TMDs) are a class of two-dimensional (2D) layered materials that exhibit a diverse range of electronic structures, including charge density waves (CDWs) that can lead to insulating, semiconducting, metallic, and even superconducting phases. While the formation of CDWs in these systems has been recognized in early research [Phys. Rev. Lett. 129, 156401 (2022); Nat. Phys. 11, 328 (2015)], the underlying mechanisms driving the commensurate CDW (CCDW) phase remain largely unexplored. CCDWs typically originate from factors such as perfect Fermi surface nesting and/or electron-phonon coupling, causing the divergence of the chiral electronic structure. However, in the case of layered 2D TMD materials with CCDW phases, the significance of reconstructed electronic structures resulting from periodic lattice distortions (PLD) and photoemission matrix element effects in the CCDW instability needs to be visualized. This study focuses on computationally accessible CCDW phases in 1T-Ta$S_2$, a prototypical TMD with a rich CDW phase diagram, aiming to understand the origins of CCDW phases. The insights gained from this investigation have the potential to advance the application of 2D materials in next-generation electronics, quantum sensing and information science.

Figures (12)

• Figure 1: Optimized geometry of (a) normal phase, (b) unit cell of 1T-Ta$S_2$. (c) $\sqrt{13}\times\sqrt{13}$ superlattice unit cell of CCDW phase and (d) Star of David (SOD) formation with periodic random lattice distortions. (e) shows the size of Brillouin zones of normal (dotted red line) and CCDW reduced reciprocal cases (dotted black lines).
• Figure 2: Electronic structures of a 1T-Ta$S_2$ normal bulk phase (a) the band structure along high symmetry directions. Side way, the total and partial DOS plot. (b) phonon dispersion plot showing soft phonon modes (negative frequency) in blue arrow heads.
• Figure 3: Wannier90 band structure along with DFT bands with PBESol functional (a) and Fermi surface elliptical pockets from side (b) and top (c) view.
• Figure 4: $\sqrt{13}\times\sqrt{13}$ superlattice unit cell of undistorted 1T-Ta$S_2$ monolayer and full cell volume relaxed distorted superlattice unit cell. The middle panel shows the atomic level periodic lattice distortions (PLD) along with respective band structures.
• Figure 5: Surface state spectra calculated from wannierTools MOSTOFI2008685 along high symmetry points M-$\Gamma$-M for CCDW and normal phase.