Nb3X8: From Weakly Correlated Obstructed Atomic to Strongly Correlated Mott Insulators

Nb3X8 (X is Cl,Br or I) are a class of layered van der Waals materials formed on a breathing-mode kagome lattice, which show a gapped electronic structure. Motivated by our previous work demonstrating that monolayer Nb3Cl8 is a Mott insulator (1), we investigate the effect of electronic correlations in bulk Nb3X8 compounds. We calculate the electronic structure via downfolded many-body models derived from first principles using the constrained Random Phase Approximation (cRPA) and solved within Cluster Dynamical Mean Field Theory (CDMFT). Our results show that the Coulomb interaction either renormalizes the band gap slightly or drives the system into a strongly correlated insulating regime, depending on the compound. These findings are further supported by our doping analysis. This work establishes Nb3X8 as a very interesting platform for investigating the transition from weak to strong electronic correlations.



(1) S. Grytsiuk, M. I. Katsnelson, E. G. C. P. van Loon, and M. Rösner. Nb3Cl8 a prototypical layered Mott-Hubbard insulator. npj Quantum Mater., January 2024.