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

Abstract

The layered Mott insulator $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{RuC}{\mathrm{l}}_{3}$ 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 $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{RuC}{\mathrm{l}}_{3}$ using scanning tunneling microscopy/spectroscopy. Characteristic tunneling spectra were detected on $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{RuC}{\mathrm{l}}_{3}$ layers in proximity to graphite. In the single-layer $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{RuC}{\mathrm{l}}_{3}$ 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 $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{RuC}{\mathrm{l}}_{3}$ 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 $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{RuC}{\mathrm{l}}_{3}$ 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 $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{RuC}{\mathrm{l}}_{3}$ and graphite is a good platform for investigating the doping physics in $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{RuC}{\mathrm{l}}_{3}$. Therefore, tunneling into such a doped system is a useful probe for studying otherwise insulating spin liquid candidates.