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The metal–insulator transition in vanadium dioxide can be reversibly suppressed to cryogenic temperatures by doping with atomic hydrogen.

Electronic nematicity, a unidirectional self-organized state that breaks the rotational symmetry of the underlying lattice, has been observed in an iron-based superconductor, BaFe₂(As_1−xP _x )₂, over a wide range of phosphorus concentration, resulting in a phase diagram similar to the pseudogap phase diagram of the copper oxides.

Quantum fluctuations in frustrated magnets are expected to produce unconventional emergent behaviour. Neutron spectroscopy measurements now provide evidence for emergent gauge fields in a pyrochlore spin ice.

Some materials can display magnetic order despite having spin-singlet ground state on individual magnetic sites. This arises due to exchange interactions mixing excited crystal electric field states. Here, Gao et al study and example of such a system, Ni₂Mo₃O₈, and find that crystal electric field states in both the paramagnetic and antiferromagnetic states exhibit dispersive excitations.

Whether an actual Mott insulator phase exists in iron pnictides remains elusive. Here, Songet al. demonstrate an antiferromagnetic insulator phase persisting above the Néel temperature in NaFe_1−xCu_xAs, indicative of a Mott insulator, highlighting the role of electron correlations in high-T_csuperconductivity.

Sc₃In and ZrZn₂ are the only two known itinerant ferromagnets that form from non-magnetic constituents. Now, Svanidze et al.,evidence itinerant antiferromagnetism in TiAu below 36 K using thermodynamic, transport, muon-based and neutron-based measurements, and density functional analysis.

A detailed neutron scattering and muon spin relaxation study uncovers a continuum of magnetic excitations down to 35 mK in the pyrochlore lattice compound Ce₂Zr₂O₇ with minimum chemical disorder, consistent with quantum spin liquid behaviour.

The nature of quantum criticality in intermetallic f-electron compounds exhibiting valence fluctuations is not well understood. Here, using a combination of experimental techniques, the authors attribute quantum criticality in YbAlB₄ to the anisotropic hybridization between the conduction and f-electrons.

The interplay between nematic, antiferromagnetic order and superconductivity in the iron pnictide superconductors remains obscured. Here, Wang et al. demonstrate well-separated nematic and Neel transition temperatures near optimal superconductivity in NaFe_1−xNi_xAs and uncover local distortions which could account for rotational symmetry breaking common in iron pnictides.

The Dicke model, describing the cooperative coupling of an ensemble of two-level atoms with a single-mode light field, has a rich phenomenology in quantum optics and quantum information, but its analytical or numerical solution is beyond current reach. Here, a solid-state quantum simulator of an extended Dicke model is achieved using ErFeO₃ crystals, where terahertz spectroscopy and magnetocaloric effect measurements reveal an atomically ordered phase in addition to the expected superradiant and normal phases.

Quantum criticality, a process driven by non-thermal parameters such as magnetic field, doping or pressure, when combined with magnetism and electron correlations, can give rise to quantum phase transitions and novel physics. Here, the authors present experimental evidence for itinerant antiferromagnetism in Ti₃Cu₄, as well as evidence of a magnetic field-induced quantum critical point.