Evidence of Mott insulator with thermally induced melting behavior in kagome compound Nb₃Cl₈

The kagome lattice provides a playground to explore novel correlated quantum states due to the presence of flat bands in its electronic structure. The recently discovered layered kagome compound Nb₃Cl₈ has been proposed as a Mott insulator coming from the half-filled flat band. Here, we have carried out a systematic transport study to uncover evidence of the Mott insulator in Nb₃Cl₈ thin flakes. A bipolar semiconducting property with Fermi level close to the conduction band has been revealed. We have further probed the chemical potential of Nb₃Cl₈ by tracing the charge neutrality point of monolayer graphene proximate to Nb₃Cl₈. The gap of Nb₃Cl₈ flakes is ∼1.10 eV at 100 K and shows pronounced temperature dependence, decreasing substantially with increasing temperature to ∼0.63 eV at 300 K. The melting behavior of the gapped state is consistent with the theoretically proposed Mott insulator in Nb₃Cl₈. Our work has demonstrated Nb₃Cl₈ as a promising platform to study strongly correlated physics at relatively high temperature.