Volume 15 Issue 5, May 2019

Einstein’s general theory of relativity is one of the most important accomplishments in the history of science. We reassess the importance of one of the expeditions that made its experimental verification possible — a story that involves a sense of adventure and scientific ingenuity in equal measure.

Ultrasonic radiation forces are harnessed to trap and then shake clusters of spheres — mimicking the effect of temperature on cluster formation in granular systems. This assembly process has applications from the nanoscale to the macroscale.

Kagome lattice materials combine a frustrated lattice with electron–electron and spin–orbit interactions. One of them, Co₃Sn₂S₂, now reveals magnetic properties that respond in the opposite way to what is expected.

One of the fundamental radioactive decay modes of nuclei is β decay. Now, nuclear theorists have used first-principles simulations to explain nuclear β decay properties across a range of light- to medium-mass isotopes, up to ¹⁰⁰Sn.

The difference between the β-decay rate predicted for free neutrons and that measured in real nuclei is explained by first-principles calculations to arise from strong correlations and the weak-force coupling between nucleons.

Spectral study on ^36,37,38Ca isotopes and calculations based on density functional theory reveal the interplay between charge radii and nucleonic pairing correlations.

The quantum Hall effect is thought to exist only in two-dimensional materials. Here, transport measurements show that thin graphite slabs have a 2.5-dimensional version, with a parity effect for samples with odd and even number of layers.

The authors show that a magnetic material with kagome lattice planes hosts a flat band near the Fermi level. Electrons in this band exhibit ‘negative magnetism’ due to the Berry curvature.

By subjecting a Chern insulator to a circular drive, its geometrical and topological properties would be accessible from the spectroscopic response. This prediction is now confirmed in a Floquet topological system realized by ultracold fermionic atoms.

Inelastic neutron scattering is used to probe the spin dynamics of molecular nanomagnets, but extensive supporting computations make the technique challenging. Proof-of-principle experiments now show that quantum computers may solve these computations efficiently.

Acoustically levitated granular particles offer a platform on which to study self-assembly in a macroscopic system. Precise acoustic tuning reveals how cluster statistics and assembly pathways change as the system moves out of equilibrium.

In the early Universe, fluctuations in the neutrino density produced a distinct shift in the temporal phase of sound waves in the primordial plasma. The size of this phase shift has now been constrained through baryon acoustic oscillation data.

Symmetry labels of materials under certain space groups can be used to indicate their band topology. Integrating that into first-principles band-structure calculations, new topological materials with a diversity of topological phenomena are discovered.

A spectral study on a ferromagnet/superconductor heterostructure reveals the interaction between the spin-wave excitations in a magnetically ordered system (magnons) and the magnetic flux quanta formed in a superconductor (fluxons).

A molecule placed in an optical microcavity behaves as a model two-level quantum system, as demonstrated via laser extinction and interaction with single photons.

The authors use surface acoustic waves, focused in a Gaussian geometry, to manipulate the spin state of divacancy defects in silicon carbide via mechanical driving. They demonstrate that shear strain is important in controlling the spin transitions.

Euglenids are unicellular swimmers that undergo striking cell body deformations, interpreted variously as locomotive or functionally redundant. Experiments now suggest that these deformations enable adaptation to a fast crawling mode when the cells are confined.

Repeated error correction creates a logical qubit encoded in the hybrid state of a superconducting circuit and a bosonic cavity, which is shown to be fully controllable under a universal single-qubit gate set.

Actomyosin networks with rapid turnover self-organize within droplets, forming a dynamic steady-state with persistent flows. The networks exhibit homogeneous, density-independent contraction, implying that active stress scales with viscosity.

Bill Phillips celebrates a beautiful reformation of the metric system, by which scientists measure the physical world, coming into effect on World Metrology Day, 20 May 2019.