Multiband charge density wave exposed in a transition metal dichalcogenide

TL;DR

This study reveals a multiband charge density wave in 2H-NbSe2, involving multiple bands and resulting in complex, out-of-phase charge modulations, expanding understanding of electronic instabilities in layered materials.

Contribution

It provides the first evidence of a multiband charge density wave in a transition metal dichalcogenide using combined STM and theoretical modeling.

Findings

Evidence of a CDW gap on both inner and outer bands.

Detection of spatially out-of-phase charge modulations.

Energy-dependent contrast in STM images confirms multiband CDW.

Abstract

In the presence of multiple bands, well-known electronic instabilities may acquire new complexity. While multiband superconductivity is the subject of extensive studies, the possibility of multiband charge density waves (CDWs) has been largely ignored so far. Here, combining energy dependent scanning tunnelling microscopy (STM) topography with a simple model of the charge modulations and a self-consistent calculation of the CDW gap, we find evidence for a multiband CDW in 2H-NbSe$_2$. This CDW not only involves the opening of a gap on the inner band around the K-point, but also on the outer band. This leads to spatially out-of-phase charge modulations from electrons on these two bands, which we detect through a characteristic energy dependence of the CDW contrast in STM images.