Uncovering the S=1/2 Kagome Ferromagnet within a Family of Metal-Organic Frameworks

[Image: see text] Kagome networks of ferromagnetically or antiferromagnetically coupled [Image: see text] magnetic moments represent important models in the pursuit of a diverse array of novel quantum and topological states of matter. Here, we explore a family of Cu(2+)-containing metal–organic frameworks (MOFs) bearing [Image: see text] kagome layers pillared by ditopic organic linkers with the general formula Cu(3)(CO(3))(2)(x)(3)·2ClO(4) (MOF-x), where x is 1,2-bis(4-pyridyl)ethane (bpe), 1,2-bis(4-pyridyl)ethylene (bpy), or 4,4′-azopyridine (azpy). Despite more than a decade of investigation, the nature of the magnetic exchange interactions in these materials remained unclear, meaning that whether the underlying magnetic model is that of an [Image: see text] kagome ferromagnet or antiferromagnet is unknown. Using single-crystal X-ray diffraction, we have developed a chemically intuitive crystal structure for this family of materials. Then, through a combination of magnetic susceptibility, powder neutron diffraction, and muon-spin spectroscopy measurements, we show that the magnetic ground state of this family consists of [Image: see text] ferromagnetic kagome layers that are coupled antiferromagnetically via their extended organic pillaring linkers

Optical antennas based on coupled nanoholes in thin metal films

The ability to control optical effects at the nanoscale is a challenge that could be of great importance for a range of photonic applications. However, progress requires a deep understanding of the relationship between near-field and far-field properties of the individual elements of the nanostructure, as well as of the role of nano-optical interactions. Here, we show that the strong interaction between nanoholes in optically thin metal films can be used to readily tune their spectral response and visibility. Control of this interaction in short chains of nanoholes enables either amplification or almost total suppression of the scattered light. The phenomena are interpreted in terms of hole coupling mediated via antisymmetric surface plasmon polaritons, which makes the nanohole chains effectively behave as linear wire antennas