Emergence of the spin polarized domains in the kagome lattice Heisenberg antiferromagnet Zn-barlowite (Zn$_{0.95}$Cu$_{0.05}$)Cu$_{3}$(OD)$_{6}$FBr

TL;DR

This study uses advanced 2D NMR techniques to reveal how small amounts of interlayer Cu defects induce spin polarized domains in a kagome lattice, affecting low-energy excitations and highlighting disorder effects in quantum spin liquids.

Contribution

It introduces a novel 2D NMR method to distinguish intrinsic kagome spin behavior from disorder effects and demonstrates the formation of spin polarized domains due to Cu defects.

Findings

Spin polarized domains occupy about 60% of the sample volume at 2 K.

Interlayer Cu defects induce gapless low-energy excitations within kagome planes.

Disorder from defects significantly influences the magnetic properties of the kagome lattice.

Abstract

Kagome lattice Heisenberg antiferromagnets are known to be highly sensitive to perturbations caused by 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 (Zn$_{0.95}$Cu$_{0.05}$)Cu$_{3}$(OD)$_{6}$FBr 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\% Cu$^{2+}$ defect spins occupying the interlayer non-magnetic Zn$^{2+}$ sites. These spin polarized domains account for $\sim60$\% 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.