The recent observation of superconductivity in hole-doped NdNiO 2 has generated considerable attention. The similarities and differences between this infinite-layer nickelates and cuprates are still an open question. To address this issue we derive, via-principles calculations, essential facts related to the electronic structure and magnetism of RNiO 2 (R ¼ La, Nd) in comparison to their cuprate analog CaCuO 2. From this detailed comparison, we find that RNiO 2 are promising as cuprate analogs. Besides the much larger d − p energy splitting, and the presence of R 5d states near the Fermi energy in the parent compound, all other electronic-structure parameters seem to be favorable in the context of superconductivity as inferred from the cuprates. In particular, the large value of the longer-range hopping t 0 and the e g energy splitting are similar to those obtained in cuprates. Doping further acts to increase the cupratelike character of these nickelates by suppressing the self-doping effect of the R 5d bands.

High temperature cuprate superconductivity remains a defining problem in condensed matter physics.Among myriad approaches to addressing this problem has been the study of alternative transition metal oxides with similar structures and 3d electron count that are suggested as proxies for cuprate physics.None of these analogs has been superconducting, and few are even metallic. Here, we report that the lowvalent, quasi-two-dimensional trilayer compound, Pr4Ni3O8 avoids a charge-stripe ordered phase previously reported for La4Ni3O8, leading to a metallic ground state. By combining x-ray absorption spectroscopy and density functional theory calculations, we further find that metallic Pr4Ni3O8 exhibits a low-spin configuration and significant orbital polarization of the unoccupied eg states with pronounced dx 2 -y 2 character near the Fermi energy, both hallmarks of the cuprate superconductors. Belonging to a regime of 3d electron count found for hole-doped cuprates, Pr4Ni3O8 thus represents one of the closest analogies to cuprates yet reported and a singularly promising candidate for high-Tc superconductivity if appropriately doped.

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Based on first principles calculations, the evolution of the electronic and magnetic properties of transition metal dihalides MX2 (M= V, Mn, Fe, Co, Ni; X = Cl, Br, I) is analyzed from the bulk to the monolayer limit. A variety of magnetic ground states is obtained as a result of the competition between direct exchange and superexchange. The results predict that FeX2, NiX2, CoCl2 and CoBr2 monolayers are ferromagnetic insulators with sizable magnetocrystalline anisotropies. This makes them ideal candidates for robust ferromagnetism at the single layer level. Our results highlight the importance of spin-orbit coupling to obtain the correct ground state. arXiv:1903.01789v1 [cond-mat.str-el]

There is increasing interest in the study of chiral degrees of freedom occurring in matter and in electromagnetic fields. Opportunities in quantum sciences will likely exploit two main areas that are the focus of this Review: (1) recent observations of the chiral-induced spin selectivity (CISS) effect in chiral molecules and engineered nanomaterials and (2) rapidly evolving nanophotonic strategies designed to amplify chiral light–matter interactions. On the one hand, the CISS effect underpins the observation that charge transport through nanoscopic chiral structures favors a particular electronic spin orientation, resulting in large room-temperature spin polarizations. Observations of the CISS effect suggest opportunities for spin control and for the design and fabrication of room-temperature quantum devices from the bottom up, with atomic-scale precision and molecular modularity. On the other hand, chiral–optical effects that depend on both spin- and orbital-angular momentum of photons could offer key advantages in all-optical and quantum information technologies. In particular, amplification of these chiral light–matter interactions using rationally designed plasmonic and dielectric nanomaterials provide approaches to manipulate light intensity, polarization, and phase in confined nanoscale geometries. Any technology that relies on optimal charge transport, or optical control and readout, including quantum devices for logic, sensing, and storage, may benefit from chiral quantum properties. These properties can be theoretically and experimentally investigated from a quantum information perspective, which has not yet been fully developed. There are uncharted implications for the quantum sciences once chiral couplings can be engineered to control the storage, transduction, and manipulation of quantum information. This forward-looking Review provides a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects and presents a vision for their possible future roles in enabling room-temperature quantum technologies.