We explore spin dynamics in Cu(1,3-bdc),
a quasi-2D topological
magnon insulator. The results show that the thermal evolution of the
Landé g factor (g) is anisotropic: g
in‑plane decreases while g
out‑of‑plane increases with increasing temperature T. Moreover, the anisotropy of the g factor
(Δg) and the anisotropy of saturation magnetization
(ΔM
s) are correlated below 4 K,
but they diverge above 4 K. We show that the electronic orbital moment
contributes to the g anisotropy at lower T, while the topological orbital moment induced by thermally
excited spin chirality dictates the g anisotropy
at higher T. Our work suggests an interplay among
topology, spin chirality, and orbital magnetism in Cu(1,3-bdc).
Spin-and charge-stripe order has been extensively studied in the superconducting cuprates, among which underdoped La2−xSrxCuO4 (LSCO) is an archetype which has static spin density wave (SDW) order at low temperatures. An intriguing, but not completely understood, phenomenon in LSCO is that the stripes are not perfectly aligned with the high-symmetry Cu-Cu directions, but are tilted. Using high-resolution neutron scattering, we find that the model material LSCO with x = 0.12 has two coexisting phases at low temperatures, one with static spin stripes and one with fluctuating spin stripes, where both phases have the same tilt angle. For the static SDW, we accurately determined the spin direction as well as the interlayer correlations. Moreover, we performed numerical calculations using the doped Hubbard model to explain the origin of the tilting of the stripes. The tilting is quantitatively accounted for with a next-nearest neighbor hopping t ′ that is anisotropic, consistent with the slight orthorhombicity of the sample. Our results highlight the success of the doped Hubbard model to describe specific details of the ground state of a real material, as well as the importance of t ′ in the Hamiltonian. These results further reveal how the stripes and superconductivity are sensitively intertwined at the level of model calculations as well as in experimental observations.
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.
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