Identification of the compressive trigonal crystal field and orbital polarization in strained monolayer α-RuCl3 on graphite

Abstract

α-RuCl3 is a tantalizing playground to search for the quantum spin liquid states with leading Kitaev term due to the conformation of Jackeli–Khaliullin mechanism. Suppressing the non-Kitaev interaction to approach the Kitaev limit is the major objective in the experimental design of Kitaev–Jackeli–Khaliullin materials, for which the practical feasibility rests on the manipulation of the exact crystalline structure. A tensile strain, leading to the further compressive trigonal field splitting which would alter the spin-orbital entangled character and tune the intrinsic hopping exchanges, has been widely proposed as the promising strategy to enhance the comparative Kitaev interaction. In this work, we preform in-depth Scan Tunneling Microscope study on the electronic patterns of strained α-RuCl3 monolayer on graphite substrate. Based on Chen’s derivative rule, a further trigonal field splitting is identified by analyzing the lateral-gradient imaging effect caused by an anisotropic tip. A spatial variation of the magnitude of trigonal crystal field due to the slight inhomogeneity of strain accords with the orbital polarization near the Mott gap. All evidences point to the facts that the compressive trigonal crystal field in the stretched α-RuCl3 monolayer lifts the degeneracy of t2g states with higher text{e}_{text{g}}' and lower a1g orbitals, and the Coulomb interactions of the text{e}_{text{g}}' orbitals take the main responsibility for the Mott effect.