Sr₃LiIrO₆: a potential quantum spin liquid candidate in the quasi-1-D d⁴ iridate family

Spin-orbit coupling (SOC) offers a large variety of novel and extraordinary magnetic and electronic properties in otherwise ‘ordinary pool’ of heavy ion oxides. Here we present a detailed study on an apparently isolated hexagonal 2H spin-chain d4 iridate Sr₃LiIrO₆ (SLIO) with geometric frustration. Our structural studies clearly reveal perfect Li-Ir chemical order with desired stoichiometry in this compound, while x-ray absorption together with x-ray photoemission spectroscopic characterizations establish pure 5+ valence of Ir. We have established

a magnetic ground state with finite Ir⁵⁺ magnetic moments in this compound, contrary to the anticipated non-magnetic J_eff = 0 state, through combined dc susceptibility, ⁷Li nuclear magnetic resonance (NMR), muon spin relaxation (μSR) and ab-initio electronic structure studies. These investigations together with ac magnetic susceptibility and specific heat measurements unravel that despite having noticeable antiferromagnetic correlation among the Ir⁵⁺ local moments, the SLIO system evades magnetic ordering down to at least 0.05 K, due to geometrical frustration, arising from the comparable nearest- and next-nearest-neighbor interchain Ir-O-O-Ir superexchange interaction strengths with opposite signs. On top of it, the zero-field (ZF) μSR analysis shows emergence of a considerable proportion of frozen spin dynamics within the background of an overall fluctuating highly correlated liquid-like magnetic state down to the lowest measured temperature of 1.7 K, possibly due to large differences in the intra- and inter-column Ir-Ir magnetic exchange interaction strengths. The linear temperature dependence of the magnetic specific heat (CM ) in the 0.05-4 K range in both zero and applied magnetic fields, plus the power-law behavior of the NMR spin-lattice relaxation rate suggest a gapless spinon density of states in this charge gapped quantum spin liquid-like ground state of Sr₃LiIrO₆.