Magnetism in spin models for depleted honeycomb-lattice iridates: Spin-glass order towards percolation

TL;DR

This paper investigates how non-magnetic doping affects the magnetic order in honeycomb iridates, revealing a transition from zigzag order to spin-glass states and proposing experimental ways to distinguish underlying models.

Contribution

It introduces a detailed analysis of doping effects on Heisenberg-Kitaev and related models, highlighting the emergence of spin-glass behavior and its dependence on percolation thresholds.

Findings

Doping replaces zigzag order with spin-glass states.

Spin-glass temperature varies with doping level.

Experimental distinction of models possible via percolation analysis.

Abstract

Iridates are characterized by a fascinating interplay of spin-orbit and electron-electron interactions. The honeycomb-lattice materials A2IrO3 (A=Na,Li) have been proposed to realize pseudospin-1/2 Mott insulating states with strongly anisotropic exchange interactions, described by the Heisenberg-Kitaev model, but other scenarios involving longer-range exchange interactions or more delocalized electrons have been put forward as well. Here we study the influence of non-magnetic doping, i.e., depleted moments, on the magnetic properties of experimentally relevant variants of the Heisenberg-Kitaev and Heisenberg J1-J2-J3 models. We generically find that the zigzag order of the clean system is replaced, upon doping, by a spin-glass state with short-ranged zigzag correlations. We determine the spin-glass temperature as function of the doping level and argue that this quantity allows to experimentally distinguish the different proposed spin models when the doping is driven across the site percolation threshold of the honeycomb lattice.