Dimensionality driven charge density wave instability in TiS$_2$

TL;DR

This study uses density functional theory to reveal that TiS$_2$ exhibits a charge density wave instability in thin layers, which can be controlled by strain, highlighting the importance of dimensionality in electronic phase transitions.

Contribution

The paper demonstrates the emergence of a charge density wave in TiS$_2$ monolayers and shows how strain can tune this instability, advancing understanding of 2D material phase behavior.

Findings

Charge density wave appears in TiS$_2$ monolayers under 4 layers.

Strain can tune the charge density wave instability.

Bulk TiS$_2$ exhibits a Kohn anomaly in phonon dispersion.

Abstract

Density functional theory and density functional perturbation theory are used to investigate the electronic and vibrational properties of TiS$_2$. Within the local density approximation the material is a semi-metal both in the bulk and in the monolayer form. Most interestingly we observe a Kohn anomaly in the bulk phonon dispersion, which turns into a charge density wave instability when TiS$_2$ is thinned to less than four monolayers. Such charge density wave phase can be tuned by compressive strain, which appears to be the control parameter of the instability.