Tunneling spectroscopic signatures of charge doping and associated Mott transition in -RuCl3 in proximity to graphite

The layered Mott insulator alpha-RuCl3 has been extensively studied as a potential Kitaev quantum spin liquid candidate. Here, by constructing heterostructures with graphite, we employed electron tunneling measurements on few-layer alpha-RuCl3 using scanning tunneling microscopy/spectroscopy. Characteristic tunneling spectra were detected on alpha-RuCl3 layers in proximity to graphite. In the single-layer alpha-RuCl3 in direct contact with graphite, distinct states in the Mott gap regime were observed. The in-gap states are demonstrated to be closely related to the electron orbitals in alpha-RuCl3 and graphite, and to be sensitive to interfacial coupling, where a hybridization at the heterointerface is hypothesized. The in-gap states are also thought of as a charge reservoir for weakly doping the alpha-RuCl3 upper layers. It demonstrated that the weak doping effect causes a considerable decrease in the Mott gap within the upper layers, suggesting that an unconventional Mott transition is occurring in these layers. The results show that the heterostructure comprising alpha-RuCl3 and graphite is a good platform for investigating the doping physics in alpha-RuCl3. Therefore, tunneling into such a doped system is a useful probe for studying otherwise insulating spin liquid candidates.