Local Real-Space View of the Achiral 1$T$-TiSe$_2$ 2 $\times$ 2 $\times$ 2 Charge Density Wave

TL;DR

This study uses advanced STM techniques to reveal the three-dimensional, achiral nature of the charge density wave in 1T-TiSe2, challenging previous claims of chiral stacking and providing new insights into its structural properties.

Contribution

It demonstrates a novel real-space approach to simultaneously probe charge and structural reconstructions in CDW materials, revealing the achiral 3D nature of the CDW in 1T-TiSe2.

Findings

Revealed the 3D achiral nature of the CDW in 1T-TiSe2

Contradicted previous claims of helical, chiral CDW stacking

Established a method for real-space structural and charge reconstruction analysis

Abstract

The transition metal dichalcogenide 1$T$-TiSe$_2$ is a quasi-two-dimensional layered material undergoing a commensurate 2 $\times$ 2 $\times$ 2 charge density wave (CDW) transition with a weak periodic lattice distortion (PLD) below $\approx$ 200 K. Scanning tunneling microscopy (STM) combined with intentionally introduced interstitial Ti atoms allows to go beyond the usual spatial resolution of STM and to intimately probe the three-dimensional character of the PLD. Furthermore, the inversion-symmetric, achiral nature of the CDW in the $z$-direction is revealed, contradicting the claimed existence of helical CDW stacking and associated chiral order. This study paves the way to a simultaneous real-space probing of both charge and structural reconstructions in CDW compounds.