Metastable Kitaev Magnets

Abstract

Nearly two decades ago, Alexei Kitaev proposed a model for spin-1/2 particles with bond-directional interactions on a two-dimensional honeycomb lattice which had the potential to host a quantum spin-liquid ground state. This work initiated numerous investigations to design and synthesize materials that would physically realize the Kitaev Hamiltonian. The first generation of such materials, such as Na2IrO3, α-Li2IrO3, and α-RuCl3, revealed the presence of non-Kitaev interactions such as the Heisenberg and off-diagonal exchange. Both physical pressure and chemical doping were used to tune the relative strength of the Kitaev and competing interactions; however, little progress was made towards achieving a purely Kitaev system. Here, we review the recent breakthrough in modifying Kitaev magnets via topochemical methods that has led to the second generation of Kitaev materials. We show how structural modifications due to the topotactic exchange reactions can alter the magnetic interactions in favor of a quantum spin-liquid phase.

High-temperature magnetic anomaly via suppression of antisite disorder through synthesis route modification in a Kitaev candidate Cu2IrO3

“…Furthermore, the Kitaev model is materialized by the superexchange interactions between spin-orbital-coupled J eff = 1/2 electrons in 4d/5d transition metal ions with a lowspin d 5 electron configuration through the Jackeli-Khaliullin mechanism [8]. In this research trend, signatures of Kitaev QSL have been captured even in realistic materials [9][10][11], and then the materials developed to realize the Kitaev QSL ground state have been vigorously promoted worldwide [12][13][14][15].…”

Disorder effects in the Kitaev-Heisenberg model

“…In addition, presence of disorder like vacancies, impurities, lattice distortions, and stacking faults, inevitable in real materials, are often responsible for the instability of QSL [12][13][14]. Recently, a new class of intercalated compounds have been synthesized which are even more susceptible to disorder H 3 LiIr 2 O 6 , Cu 2 IrO 3 , and Ag 3 LiIr 2 O 6 [15,16]. Role of disorder in Kitaev materials has gained special interest since the experimental observation of low temperature divergence in specific heat of the proximate Kitaev material, H 3 LiIr 2 O 6 , is understood as the consequence of bond disorder in the Kitaev model [17,18].…”