No abstract

Ag3LiIr2O6 is a Kitaev spin liquid candidate material synthesised from α-Li2IrO3 through a topotactic reaction. We investigate the structural and magnetic properties of two samples of Ag3LiIr2O6 based on 7 Li nuclear magnetic resonance line shape, Knight shift and spin-lattice relaxation rate 1/T1. The first sample A shows signatures of magnetically ordered spins, and exhibits one sharp 7 Li peak with FWHM increasing significantly below 14 K. 1/T1 of this sample displays a broad local maximum at 40 K, followed by a very sharp divergent behaviour at TN = 9 ± 1 K when bulk magnetic long range order sets in. In order to investigate the influence of structural disorder, we compare these NMR results for a second sample B, which has been shown by transmission electron microscope to have unwanted Ag inclusion at Li and Ir sites within the Ir honeycomb planes. The sample B displays an additional NMR peak with relative intensity of ∼ 17%. The small Knight shift and 1/T1 of these defect-induced 7 Li sites suggest that Ir spins in their vicinity become only weakly magnetic at low temperatures, leading to an apparent spin liquid like behaviour. We use numerical Inverse Laplace Transform T1 (ILTT1) analysis based on Tikhonov regularization to determine the distribution of 1/T1 and compare the results between the two samples.

There has been considerable recent progress in identifying candidate materials for the transversefield Ising chain (TFIC), a paradigmatic model for quantum criticality. Here, we study the local spin dynamical structure factor of different spin components in the quantum disordered region of the TFIC. We show that the low-frequency local dynamics of the spins in the Ising-and transverse-field directions have strikingly distinctive temperature dependencies. This leads to the thermal-activation gap for the secular term of the nuclear magnetic resonance (NMR) 1/T 2 relaxation rate to be half of that for the 1/T1 relaxation rate. Our findings reveal a new surprise in the nonzero-temperature dynamics of the venerable TFIC model and uncover a means to evince the material realization of the TFIC universality.

Kagome lattice Heisenberg antiferromagnets are known to be highly sensitive to perturbations caused by the structural disorder. NMR is a local probe ideally suited for investigating such disorder-induced effects, but in practice, large distributions in the conventional one-dimensional NMR data make it difficult to distinguish the intrinsic behavior expected for pristine kagome quantum spin liquids from disorder-induced effects. Here we report the development of a two-dimensional NMR data acquisition scheme applied to Zn-barlowite (Zn0.95Cu0.05)Cu3(OD)6FBr kagome lattice, and successfully correlate the distribution of the low energy spin excitations with that of the local spin susceptibility. We present evidence for the gradual growth of domains with a local spin polarization induced by 5% Cu2+ defect spins occupying the interlayer non-magnetic Zn2+ sites. These spin-polarized domains account for ~60% of the sample volume at 2 K, where gapless excitations induced by interlayer defects dominate the low-energy sector of spin excitations within the kagome planes.

No abstract