Direct identification of Mott Hubbard band pattern beyond charge density wave superlattice in monolayer 1T-NbSe2

TL;DR

This study uses scanning tunneling microscopy/spectroscopy to explore the electronic structure of monolayer 1T-NbSe2, revealing the spatial distribution of the Mott upper Hubbard band and its relation to charge density wave patterns.

Contribution

It provides new insights into the spatial distribution of the Mott Hubbard band and its relationship with charge density waves in monolayer 1T-NbSe2, beyond traditional charge density wave superlattice understanding.

Findings

UHB is spatially distributed away from the dz2 orbital.

UHB exhibits a root3 x root3 R30° periodicity.

CDW patterns are visible deep in the Mott gap without Mott Hubbard band contribution.

Abstract

Understanding Mott insulators and charge density waves (CDW) is critical for both fundamental physics and future device applications. However, the relationship between these two phenomena remains unclear, particularly in systems close to two-dimensional (2D) limit. In this study, we utilize scanning tunneling microscopy/spectroscopy to investigate monolayer 1T-NbSe2 to elucidate the energy of the Mott upper Hubbard band (UHB), and reveal that the spin-polarized UHB is spatially distributed away from the dz2 orbital at the center of the CDW unit. Moreover, the UHB shows a root3 x root3 R30{\deg} periodicity in addition to the typically observed CDW pattern. Furthermore, a pattern similar to the CDW order is visible deep in the Mott gap, exhibiting CDW without contribution of the Mott Hubbard band. Based on these findings in monolayer 1T-NbSe2, we provide novel insights into the relation between the correlated and collective electronic structures in monolayer 2D systems.