Thermodynamic Evidence of Proximity to a Kitaev Spin Liquid in Ag3LiIr2O6

Abstract

Kitaev magnets are materials with bond-dependent Ising interactions between localized spins on a honeycomb lattice. Such interactions could lead to a quantum spin-liquid (QSL) ground state at zero temperature. Recent theoretical studies suggest two potential signatures of a QSL at finite temperatures, namely a scaling behavior of thermodynamic quantities in the presence of quenched disorder, and a two-step release of the magnetic entropy. Here, we present both signatures in Ag3LiIr2O6 which is synthesized from α-Li2IrO3 by replacing the inter-layer Li atoms with Ag atoms. In addition, the DC susceptibility data confirm absence of a long-range order, and the AC susceptibility data rule out a spin-glass transition. These observations suggest a closer proximity to the QSL in Ag3LiIr2O6 compared to its parent compound α-Li2IrO3 that orders at 15 K. We discuss an enhanced spin-orbit coupling due to a mixing between silver d and oxygen p orbitals as a potential underlying mechanism.

Anderson–Kitaev spin liquid

“…Indeed, experiments in A 3 LiIr 2 O 6 (A = H, Ag, etc.) show a universal scaling in the field dependence of the heat capacity 5,18 , which strongly suggests the existence of disorder 19,20 . The candidate ground states must be disordered QSLs, and the absence of long-range order can be attributed to the critical role of disorder.…”

“…Thus, this study is not only a model investigation for the disordered Kitaev materials like A 3 LiIr 2 O 6 (A = H, D, Ag, etc.) 5,18,22 , but also a systematic examination of a numerically solvable disordered QSL, which would be an attempt towards the universal understanding of various disordered QSLs. Especially, since most QSLs are unsolvable, an unbiased study of disordered QSLs was impossible in the previous method.…”

Effect of structural disorder on the Kitaev magnet Ag3LiIr2O6

“…Ag 3 LiIr 2 O 6 was synthesized via a topotactic cationexchange reaction as reported in Ref. [14]. To improve the sample quality, however, we took two important additional measures.…”

“…It has been claimed that this new family of Kitaev magnets, specifically H 3 LiIr 2 O 6 and Ag 3 LiIr 2 O 6 , are closer to the QSL phase based on the absence of magnetic ordering in thermodynamic measurements, scaling behavior in the heat capacity, and a two-step release of the magnetic entropy [11,14,16,17]. Both bond disorder and modified interlayer coordination have been hypothesized as possible mechanisms for the proximity to the QSL ground state [13,14,17,18]. Currently, there is no careful experimental work to examine these hypotheses and elucidate the role of structural disorder in the intercalated Kitaev magnets.…”

“…Second, we also reveal a peak in the heat capacity of S1 at T N , which turns into a mild change in slope in S2. In light of these findings, we will revisit the two-step entropy release that has been interpreted as evidence of spin fractionalization in Ag 3 LiIr 2 O 6 , α-Li 2 IrO 3 , Na 2 IrO 3 , and α-RuCl 3 [14,19,20]. Third, using muon spin relaxation (μSR) measurements, we show that T N marks the onset of an incommensurate magnetic order with short-range correlations that become long range below T LRO in the clean sample, S1.…”