Direct evidence of intrinsic Mott state and its layer-parity oscillation in a breathing kagome crystal down to monolayer

TL;DR

This study provides direct spectroscopic evidence of Mott insulating states in layered Nb3Cl8, revealing layer-dependent oscillations in electronic states and advancing atomic-scale LDOS mapping techniques for insulating materials.

Contribution

It demonstrates the persistence of Mott states down to monolayer Nb3Cl8 and uncovers layer-parity oscillations in the local density of states, supported by advanced STM and theoretical analysis.

Findings

Mott bands persist in monolayer Nb3Cl8

Layer-parity oscillation in LDOS between even and odd layers

Technical advance in atomic-scale LDOS mapping for insulators

Abstract

We report direct spectroscopic evidence of correlation-driven Mott states in layered Nb$_3$Cl$_8$ through combining scanning tunneling microscopy (STM) and dynamical mean-field theory. The Hubbard bands persist down to monolayer, providing the definitive evidence for the Mottness in Nb$_3$Cl$_8$. While the size of the Mott gap remains almost constant across all layers, a striking layer-parity-dependent oscillation emerges in the local density of states (LDOS) between even (n = 2,4,6) and odd layers (n = 1,3,5), which arises from the dimerization and correlation modulation of the obstructed atomic states, respectively. Our conclusions are supported by a critical technical advance in atomic-scale LDOS mapping for highly insulating systems. This work provides the definitive experimental verification of correlation-driven Mott ground states in Nb3Cl8 while establishing a general protocol for investigating the interplay of electronic correlation and interlayer coupling in layered insulators by using low-temperature STM technique.