Speaker
Description
Understanding how electron correlations intertwine with topological properties of a crystal structure is a central challenge in quantum materials research. In this talk, I will discuss the family of breathing kagome compounds Nb3X8 (X = F, Cl, Br, I) as a versatile platform for exploring this interplay. Building on our recent work, I will first show how monolayer Nb3Cl8 constitutes an almost ideal realization of a single-orbital Mott–Hubbard insulator when described in a molecular orbital basis, with its low-energy physics fully captured by a one-band Hubbard model. I will then extend this perspective to the broader Nb3X8 series, where ab initio downfolding combined with cluster dynamical mean-field theory reveals a systematic evolution from weakly to strongly correlated states across the halogen series. The low-temperature bulk phases display tunable Coulomb- and Mott-driven gaps, suppressed electron–phonon coupling, and interlayer dimerization effects that yield magnetically singlet-like ground states. Finally, I will outline how these correlation-driven symmetry-breaking phenomena in Nb3X8 can influence quantum transport, providing new insights into the recently observed field-free Josephson diode effect in NbSe2/Nb3X8/NbSe2 heterojunctions. This connection highlights how correlated kagome systems can serve as a versatile platform for emergent functionalities in many-body driven devices.