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Rare earth Nickelates, (RENiO₃) host a bond disproportionation phase transition where oxygen 2p holes form at one of the Ni sites. This process results in a spin-disproportionation state where a singlet state is formed by the spin of the nickel and the spin of the oxygen hole at every other site. Here, Li et al find evidence of this spin-disproportionated state in a rareearth nickelate.

The critical temperature of most superconductors varies with the density of charge carriers, which in turn is most easily tuned by chemical doping. The observation that a specially fabricated two-dimensional superconductor maintains the same critical temperature regardless of doping raises some important questions.

Phonon polaritons are promising for infrared applications while it is difficult to tune the phonon polariton properties. Here, authors report a thermal and electrostatic tuning of surface phonon polaritons in heterostructures of LaAlO3/SrTiO3.

A century ago, Heike Kamerlingh Onnes discovered superconductivity. And yet, despite the conventional superconductors being understood, the list of unconventional superconductors is growing — for which unconventional theories may be required.

In the pseudogap phase of a high-temperature cuprate superconductor, conflicting evidence from different experiments points to a competing state or a precursor-to-superconductivity state. One single experiment now determines that both states exist.

Emergent quanta of momentum and charge, called quasiparticles, govern many of the properties of materials. The development of a quasiparticle collider promises to reveal fundamental insights into these peculiar entities. See Letter p.225

The rotation of polarized light in certain materials when subject to a magnetic field is known as the Faraday effect. Remarkably, just one atomic layer of graphene exhibits Faraday rotations that would only be measurable in other materials many hundreds of micrometres thick.

The non-superconducting state of a high-temperature superconductor is in many ways more anomalous than the superconducting state. Unlike a standard metal, the 'normal' state shows possible signs that adding or removing one electron affects all the others.

A long-standing puzzle in the quantum critical behavior of cuprate superconductors has been the observed sub-linear power-law dependence of optical conductivity. Here, the authors present measurements of the optical spectra and resistivity of La_2−xSr_xCuO₄, and develop a theoretical framework that yields a unified description of the optical spectra, resistivity and specific heat.

Genome-wide association studies are used to identify common genetic variants that affect the structure of selected subcortical regions of the human brain; their identification provides insight into the causes of variability in brain development and may help to determine mechanisms of neuropsychiatric dysfunction.

The authors defined a roadmap for investigating the genetic covariance between structural or functional brain phenotypes and risk for psychiatric disorders. Their proof-of-concept study using the largest available common variant data sets for schizophrenia and volumes of several (mainly subcortical) brain structures did not find evidence of genetic overlap.

Understanding how the high-energy physics of Mott-like excitations affects condensate formation is a key challenge in high-temperature superconductivity. Giannettiet al. clarify the relationship of many-body CuO₂excitations and the onset of superconductivity using a new optical pump supercontinuum-probe technique.

Two-dimensional electron systems in oxide heterostructures have complex interactions that, once well understood, are expected to result in a powerful platform for electronic devices. Luo et al. show how near-field optical microscopy can perform high-resolution imaging of conducting regions in LaAlO₃/SrTiO₃ interfaces.

Colour change in many vertebrates originates from pigment dispersion or aggregation. Here, Teyssier et al. show that chameleons rapidly shift colour through a physical mechanism involving a lattice of nanocrystals in dermal iridophores, a second and deeper iridophore layer strongly reflects near-infrared light.

Transport and optical conductivity measurements reveal the non-Fermi liquid behaviour in correlated semimetal Nd₂Ir₂O₇. The result implies the emergent collective charge transport in this compound, not reconcilable with conventional band theory.