Influence of Dimensionality on the Charge Density Wave Phase of 2H-TaSe$_{2}$

TL;DR

This study uses density functional theory to explore how the charge density wave phase in 2H-TaSe₂ varies with thickness, revealing the significant role of dimensionality and van der Waals interactions in its structural and spectral properties.

Contribution

The paper provides a detailed DFT-based analysis of how the CDW state in TaSe₂ evolves from monolayer to bulk, emphasizing the impact of interlayer interactions.

Findings

vdW effects are strongest in bulk TaSe₂ within 165-215 cm⁻¹ spectral range

Phonon spectra match experimental Raman data across different layers and temperatures

Thickness-dependent structural models accurately describe CDW formation

Abstract

Metallic transition metal dichalcogenides like tantalum diselenide (TaSe$_{2}$) exhibit exciting behaviors at low temperatures, including the emergence of charge density wave (CDW) states. In this work, density functional theory (DFT) is used to investigate how structural, electronic, and Raman spectral properties of the CDW configuration change as a function of thickness. Such findings highlight the influence of dimensionality change (from 2D to 3D) and van der Waals (vdW) interactions on the system properties. The vdW effect is most strongly present in bulk TaSe$_{2}$ in the spectral range 165 cm$^{-1}$ to 215 cm$^{-1}$. The phonons seen in the experimental Raman spectra are compared with the results calculated from the DFT models as a function of temperature and layer number. The matching of data and calculations substantiates the model's description of the CDW structural formation as a function of thickness, which is shown in depth for 1L through 6L systems. These results highlight the importance of understanding interlayer interactions, which are pervasive in many quantum phenomena involving two-dimensional confinement.