Motivated by recent experimental and numerical progress on various cluster Mott insulators, we study an extended Hubbard model on a breathing kagome lattice with a single electron orbital and $1/6$ electron filling. Two distinct types of cluster localization are found in the cluster Mott regime due to the presence of the electron repulsion between neighboring sites, rather than from the on-site Hubbard interaction in the conventional Mott insulators. We introduce a unified parton construction framework to accommodate both types of cluster Mott insulating phase as well as a trivial Ferm liquid metal and discuss the phase transitions in the phase diagram. It is shown that, in one of the cluster localization phases, the strong intersite repulsion results into locally metallic behavior within one of two triangular clusters on the breathing kagome lattice. We further comment on experimental relevance to existing Mo-based cluster magnets.

• Received 25 August 2020
• Revised 11 October 2020
• Accepted 24 November 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.043424

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Published by the American Physical Society