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.