Tunneling spectroscopic signatures of charge doping and Mott-phase transition in ${\alpha}$-RuCl${_3}$ in proximity to graphite

Abstract

Layered Mott insulator ${\alpha}$-RuCl${_3}$ has been intensely investigated as a possible candidate for Kitaev quantum spin liquid. In this letter, we report electron tunneling measurements on few-layer ${\alpha}$-RuCl${_3}$ in proximity to graphite, using a scanning tunneling microscopy. Signatures of charge doping have been observed in ${\alpha}$-RuCl${_3}$ layers stacking on the surface of graphite. Upon charge doping, we observed characteristic tunneling spectra that are dependent on the number of layers of ${\alpha}$-RuCl${_3}$. For a single ${\alpha}$-RuCl${_3}$ layer that is in direct contact with graphite, data shows charge states emerging in the Mott-gap regime with conservation of the Hubbard bands. For a bilayer of ${\alpha}$-RuCl${_3}$, data indicates an unconventional Mott-phase transition, where the Hubbard bands collapse accompanied by a dramatical gap-reduction. The results have thus demonstrated that tunneling into doped few-layer ${\alpha}$-RuCl${_3}$ is a useful probe to investigate this otherwise insulating spin-liquid candidate, providing fundamental information concerning electronic properties and theoretically proposed strong correlation physics in ${\alpha}$-RuCl${_3}$.Comment: Original data are available upon resonable request from corresponding autho