Revealing the Charge Density Wave caused by Peierls instability in two-dimensional NbSe$_{2}$

TL;DR

This paper investigates the origin of charge density waves in 2D NbSe2, demonstrating that Peierls instability, rather than Fermi surface nesting, causes the CDW state through first-principles calculations and STM analysis.

Contribution

It provides evidence that the CDW in 2D NbSe2 is driven by Peierls instability, clarifying the role of Fermi surface nesting in this process.

Findings

Filled phase exhibits fully opened gaps at the CDW Brillouin zone boundary.

Fermi surface nesting involves two vectors in the normal phase.

Single nesting vector leads to stripe phase formation.

Abstract

The formation of a charge density wave (CDW) in two-dimensional (2D) materials caused by Peierls instability is a controversial topic. This study investigates the extensively debated role of Fermi surface nesting in causing the CDW state in 2H-NbSe$_{2}$ materials. Four NbSe$_{2}$ structures (i.e., normal, stripe, filled, and hollow structures) are identified on the basis of the characteristics in scanning tunneling microscopy images and first-principles simulations. The calculations reveal that the filled phase corresponds to Peierls' description; that is, it exhibits fully opened gaps at the CDW Brillouin zone boundary, resulting in a drop at the Fermi level in the density of states and the scanning tunneling spectroscopy spectra. The electronic susceptibility and phonon instability in the normal phase indicate that the Fermi surface nesting is triggered by two nesting vectors, whereas the involvement of only one nesting vector leads to the stripe phase. This comprehensive study demonstrates that the filled phase of NbSe$_{2}$ can be categorized as a Peierls-instability-induced CDW in 2D systems.