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

TL;DR

This study uses tunneling spectroscopy on heterostructures of ${\alpha}$-RuCl${_3}$ and graphite to reveal charge doping effects and an unconventional Mott transition, providing insights into the material's electronic and magnetic properties.

Contribution

It demonstrates the use of heterostructure tunneling spectroscopy to observe charge doping and Mott transition signatures in ${\alpha}$-RuCl${_3}$, a candidate Kitaev spin liquid.

Findings

In-gap states are related to interfacial hybridization.

Weak doping reduces the Mott gap in upper layers.

Heterostructures serve as platforms to study doping physics.

Abstract

The layered Mott insulator ${\alpha}$-RuCl${_3}$ 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 ${\alpha}$-RuCl${_3}$ using a scanning tunneling microscopy/spectroscopy. Characteristic tunneling spectra were detected on ${\alpha}$-RuCl${_3}$ layers in proximity to graphite. In the single-layer ${\alpha}$-RuCl${_3}$ 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 ${\alpha}$-RuCl${_3}$ 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 ${\alpha}$-RuCl${_3}$ 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 comprised of ${\alpha}$-RuCl${_3}$ and graphite is a good platform for investigating the doping physics in ${\alpha}$-RuCl${_3}$. Therefore, tunneling into such a doped system is a useful probe for studying otherwise insulating spin-liquid candidates.