Lattice-Driven Electronic Structure Reconstruction in the Commensurate CDW Phase of 1T-Ta$S_2$

TL;DR

This study uses DFT and tight-binding models to connect lattice distortions with electronic structure changes in the CCDW phase of 1T-TaS2, revealing how band folding and Fermi surface reconstruction occur.

Contribution

It provides a detailed microscopic framework linking lattice distortions to electronic structure changes in 1T-TaS2's CCDW phase, emphasizing band folding effects.

Findings

Lattice relaxation leads to Star-of-David distortion consistent with phonon softening.

Band folding from Brillouin zone reduction causes Fermi surface reconstruction.

Features attributed to Fermi surface nesting emerge naturally from lattice-induced band folding.

Abstract

We investigate the structural and electronic reconstruction associated with the commensurate charge-density-wave (CCDW) phase in bulk and monolayer 1T-TaS2 using density functional theory (DFT) and Wannier-based tight-binding modeling. Structural relaxation of a sqrt(13) x sqrt(13) supercell leads spontaneously to the formation of the Star-of-David (SoD) distortion, consistent with phonon softening of the undistorted phase. We focus on establishing a direct connection between real-space lattice distortion and momentum-space electronic reconstruction. Using Wannier interpolation, we demonstrate how the CCDW-induced Brillouin zone reduction leads to band folding, narrowing of Ta 5d bands, and reconstruction of the Fermi surface. Our analysis shows that features often interpreted as Fermi surface nesting emerge naturally from band folding associated with lattice distortion. We compare our calculated electronic structure with previously reported angle-resolved photoemission spectroscopy (ARPES) results at a qualitative level. While we do not explicitly compute electronic susceptibility or electron-phonon coupling matrix elements, the results provide a consistent microscopic framework linking lattice instability and electronic structure reconstruction in 1T-TaS2.