First demonstration of tuning between the Kitaev and Ising limits in a honeycomb lattice.

Bahrami, Faranak; Hu, Xiaodong; Du, Yonghua; Lebedev, Oleg I; Wang, Chennan; Luetkens, Hubertus; Fabbris, Gilberto; Graf, Michael J et al. · Sci Adv · 2022

basic_science · Level V

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Abstract

Recent observations of novel spin-orbit coupled states have generated interest in 4<i>d</i>/5<i>d</i> transition metal systems. A prime example is the [Formula: see text] state in iridate materials and α-RuCl<sub>3</sub> that drives Kitaev interactions. Here, by tuning the competition between spin-orbit interaction (λ<sub>SOC</sub>) and trigonal crystal field (Δ<sub>T</sub>), we restructure the spin-orbital wave functions into a previously unobserved [Formula: see text] state that drives Ising interactions. This is done via a topochemical reaction that converts Li<sub>2</sub>RhO<sub>3</sub> to Ag<sub>3</sub>LiRh<sub>2</sub>O<sub>6</sub>. Using perturbation theory, we present an explicit expression for the [Formula: see text] state in the limit Δ<sub>T</sub> ≫ λ<sub>SOC</sub> realized in Ag<sub>3</sub>LiRh<sub>2</sub>O<sub>6</sub>, different from the conventional [Formula: see text] state in the limit λ<sub>SOC</sub> ≫ Δ<sub>T</sub> realized in Li<sub>2</sub>RhO<sub>3</sub>. The change of ground state is followed by a marked change of magnetism from a 6 K spin-glass in Li<sub>2</sub>RhO<sub>3</sub> to a 94 K antiferromagnet in Ag<sub>3</sub>LiRh<sub>2</sub>O<sub>6</sub>.