Unconventional anisotropic charge dynamics in bulk $1T$-TaS$_2$ induced by interlayer dimerization

TL;DR

This study reveals that in bulk $1T$-TaS$_2$, charge dynamics are highly anisotropic due to interlayer dimerization, with in-plane electronic structure reconstructed by lattice distortion and out-of-plane behavior driven by Peierls-like dimerization, clarifying the metal-insulator transition mechanism.

Contribution

It demonstrates that interlayer dimerization, not electronic correlations, primarily drives the metal-insulator transition in bulk $1T$-TaS$_2$ through anisotropic charge dynamics.

Findings

In-plane electronic structure is reconstructed by $ ext{sqrt}(13) imes ext{sqrt}(13)$ distortion.

Out-of-plane response is governed by Peierls-like dimerization.

Dimerization is the dominant mechanism of the metal-insulator transition.

Abstract

The commensurate charge-density-wave phase of the prototypical transition metal dichalcogenide $1T$-TaS$_2$ is investigated by temperature- and polarization-dependent infrared spectroscopy, revealing distinct charge dynamics parallel and perpendicular to the layers. Supported by density-functional-theory calculations, we show that the in-plane electronic structure in the low-temperature commensurate phase is reconstructed by the $\sqrt{13}\times\sqrt{13}$ distortion of the Ta layers. In contrast, the out-of-plane response is governed by a quasi-one-dimensional, Peierls-like dimerization of the two-dimensional star-of-David layers. Our results identify this dimerization as the dominant mechanism of the metal-to-insulator transition in both directions, ruling out a significant role of electronic correlations.