Anisotropic Kitaev Spin Glass in Li$_{2}$Ru$_{x}$Ir$_{1-x}$O$_{3}$

TL;DR

This study demonstrates that dilute magnetic disorder in Li$_{2}$Ru$_{x}$Ir$_{1-x}$O$_{3}$ stabilizes an anisotropic Kitaev spin glass, revealing insights into the frustrated magnetic interactions related to quantum spin liquids.

Contribution

It introduces the concept of a Kitaev spin glass stabilized by weak disorder, providing a new phase to explore in Kitaev materials.

Findings

Weak magnetic disorder suppresses magnetic order.

Anisotropic Kitaev spin glass is stabilized.

Directional anisotropy observed in magnetic properties.

Abstract

Kitaev iridates have been proposed as candidates for realizing an elusive quantum spin liquid (QSL) state, in which strong spin-orbit coupling and bond-directional exchange generate a highly frustrated and entangled ground state. However, all physical systems proposed to host this ground state, including Li$_2$IrO$_3$, Na$_2$IrO$_3$, and RuCl$_3$, develop magnetic order at low temperatures due to competing interactions. Nonetheless, theoretical modeling of experimental data has shown that Kitaev interactions are still present, motivating the application of perturbations such as pressure, magnetic field, and chemical doping to drive the system into the QSL phase. Here we study $\beta$-Li$_{2}$Ru$_{x}$Ir$_{1-x}$O$_{3}$ with dilute levels of Ru, $x \lesssim 10\%$. Through a combination of magnetometry, resonant elastic X-ray scattering, ac-heat capacity, and muon spin relaxation/resonance, we show that weak magnetic disorder suppresses long-range antiferromagnetic order and stabilizes an anisotropic spin glass that retains key signatures of Kitaev exchange. This Kitaev spin glass shows pronounced directional anisotropy in its magnetic susceptibility and thermoremenant magnetization. These results demonstrate that dilute magnetic disorder can access an anisotropic Kitaev spin glass: a proximate phase that freezes the Kitaev frustration landscape. This could provide a new window into the degeneracy, anisotropy, and competing interactions underlying the Kitaev QSL.