The thermal Hall effect of phonons does not yet have a definitive explanation. Now a careful study of doped Sr₂IrO₄ suggests that the mechanism involves the scattering of phonons by impurities embedded in an antiferromagnetic environment.

Heterostructures of transition metal dichalcogenides are known to simulate the triangular-lattice Hubbard model. Now, by combining a monolayer and bilayer of different materials, this idea is extended to multi-orbital Hubbard models.

Understanding the three-dimensional nature of fracture formation and dynamics is challenging. Experiments now show that a fracture front, after originating at a particular locus in a material, propagates jump-wise and expands transversely at high speed.

Physical ageing in glassy materials can be described in a linear way through the concept of material time. Multispeckle dynamic light scattering is now shown to provide experimental access to the material time, in terms of which fluctuations become statistically reversible.

Most quantum simulations of spin models with trapped ions have been restricted to one dimension. Now, tunable simulations of Ising models with single-site detection have been demonstrated in two-dimensional ion crystals.

Observations of strong electron correlation effects have been mostly confined to compounds containing f orbital electrons. Now, the study of the 3d pyrochlore metal CuV₂S₄ reveals that similar effects can be induced by flat-band engineering.

Quantum technologies change our notion of measurement. Chenyu Wang elaborates on how quantum squeezing enhances the precision of gravitational-wave interferometers.

Two-dimensional crystals have revolutionized fundamental research across a staggering range of disciplines. We take stock of the progress gained after twenty years of work.

Quantum hypothesis testing—the task of distinguishing quantum states—enjoys surprisingly deep connections with the theory of entanglement. Recent findings have reopened the biggest questions in hypothesis testing and reversible entanglement manipulation.

The hectare has a long association with the metric system, but its most recent status has created some ambiguity as to its future application. Richard Brown surveys the lay of the land.