Monolayer 1T-NbSe2 as a 2D correlated magnetic insulator

TL;DR

This paper reports the successful synthesis of monolayer 1T-NbSe2 as a 2D correlated magnetic insulator, revealing its charge-transfer insulating nature and magnetic interactions through advanced microscopy and theoretical analysis.

Contribution

It demonstrates controlled growth of single-phase 1T-NbSe2 and provides experimental and theoretical evidence of its correlated insulating and magnetic properties.

Findings

1T-NbSe2 is a charge-transfer insulator with a Hubbard band above the valence band.

Evidence of magnetic exchange interactions via Kondo and Yu-Shiba-Rusinov states.

Successful growth of monolayer 1T-NbSe2 using MBE.

Abstract

Monolayer group-V transition metal dichalcogenides in their 1T phase have recently emerged as a platform to investigate rich phases of matter, such as spin liquid and ferromagnetism, resulting from strong electron correlations. Although 1T phase NbSe2 does not occur naturally in bulk form, it has been discovered that the 1T and 1H phases can coexist when monolayer NbSe2 is grown via molecular beam epitaxy (MBE). This discovery has inspired theoretical investigations predicting collective phenomena such as ferromagnetism in two dimensions. Here, by controlling the MBE growth parameters, we demonstrate the successful growth of single-phase 1T-NbSe2. By combining scanning tunneling microscopy/spectroscopy and ab initio calculations, we show that this system is a charge-transfer insulator, with the upper Hubbard band located above the valence band maximum. Furthermore, by creating a vertical 1T/2H NbSe2 heterostructure, we find evidence of exchange interactions between the localized magnetic moments in 1T phase and the metallic/superconducting phase, as manifested by Kondo resonances and Yu-Shiba-Rusinov bound states.