NbSe$_{2}$'s charge density wave collapse in the (LaSe)$_{1.14}$(NbSe$_{2}$)$_{2}$ misfit layer compound

TL;DR

This study reveals that in the misfit compound (LaSe)$_{1.14}$(NbSe$_{2}$)$_{2}$, charge density wave order in NbSe$_{2}$ collapses due to doping, as shown by Raman spectroscopy and first-principles calculations, indicating a doping-driven suppression of CDW.

Contribution

The paper provides the first combined experimental and theoretical analysis of lattice dynamics and CDW suppression in a misfit layered compound using Raman spectroscopy and first-principles calculations.

Findings

NbSe$_2$'s CDW collapses with doping in the misfit compound.

No CDW signature detected down to 8 K.

Lattice dynamics are derived from subunit properties and doping effects.

Abstract

Misfit layer compounds, heterostructures composed by a regular alternating stacking of rocksalt monochalcogenides bilayers and few-layer transition metal dichalchogenides, are an emergent platform to investigate highly doped transition metal dichalcogenides. Among them, (LaSe)$_{1.14}$(NbSe$_2$)$_2$ displays Ising superconductivity, while the presence of a charge density wave (CDW) in the material is still under debate. Here, by using polarized Raman spectroscopy and first-principles calculations, we show that NbSe$_2$ undergoes a doping-driven collapse of the CDW ordering within the misfit, and no signature of the CDW is detected down to 8~K. We provide a complete experimental and theoretical description of the lattice dynamics of this misfit compound. We show that the vibrational properties are obtained from those of the two subunits, namely the LaSe unit and the NbSe$_2$ bilayer, in the presence of a suitable field-effect doping, and then highlight the 2D nature of the lattice dynamics of NbSe$_2$ within the (LaSe)$_{1.14}$(NbSe$_2$)$_2$ 3D structure.