Kitaev magnetism in honeycomb RuCl3 with intermediate spin-orbit coupling

TL;DR

This paper demonstrates that Kitaev interactions can arise in honeycomb RuCl3 with intermediate spin-orbit coupling, driven by electron correlations, leading to a potential realization of Kitaev physics beyond iridium oxides.

Contribution

It reveals how Kitaev interactions emerge in 4d RuCl3 despite weaker SOC, through correlation effects, expanding the scope of materials for Kitaev physics.

Findings

Kitaev interactions are present in RuCl3 due to correlation effects.

The derived spin model shows large antiferromagnetic Kitaev and ferromagnetic Heisenberg interactions.

The ground state is close to a Kitaev spin liquid with zigzag order.

Abstract

Intensive studies of the interplay between spin-orbit coupling (SOC) and electronic correlations in transition metal compounds have recently been undertaken. In particular, $j_{\rm eff}$ = 1/2 bands on a honeycomb lattice provide a pathway to realize Kitaev's exactly solvable spin model. However, since current wisdom requires strong atomic SOC to make $j_{\rm eff}=1/2$ bands, studies have been limited to iridium oxides. Contrary to this expectation, we demonstrate how Kitaev interactions arise in 4$d$-orbital honeycomb $\alpha$-RuCl$_3$, despite having significantly weaker SOC than the iridium oxides, via assistance from electron correlations. A strong coupling spin model for these correlation-assisted $j_{\rm eff}$ = 1/2 bands is derived, in which large antiferromagnetic Kitaev interactions emerge along with ferromagnetic Heisenberg interactions. Our analyses suggest that the ground state is a zigzag-ordered phase lying close to the antiferromagnetic Kitaev spin liquid. Experimental implications for angle resolved photoemission spectroscopy, neutron scattering, and optical conductivities are discussed.