Letters in 2016

When general relativity is included in large-scale simulations of the cosmic structure of the Universe, relativistic effects turn out to be small but measurable, thus providing tests for models of dark matter and dark energy.

Multidimensional protein-folding dynamics are often probed experimentally by projecting into a single dimension. Single-molecule experiments now verify the idea that folding can be understood in terms of one-dimensional diffusion over a landscape.

The stability of a large class of elemental knots and links to so-called reconnections is studied numerically using the Gross–Pitaevskii model for a superfluid, demonstrating that they universally untie.

Spin–orbit coupling in two dimensions is essential for observing topological phases in ultracold atoms. Such a coupling was produced in a gas of potassium atoms and a robust Dirac point was observed in the energy dispersions of the dressed atoms.

Coherent valley exciton dynamics are directly probed in a monolayer transition metal dichalcogenide, providing access to the valley coherence time and decoherence mechanisms — crucial for developing methods for manipulating the valley pseudospin.

The magnetic response of nanoparticles made from wide-bandgap oxides that don’t contain any magnetic cations is somewhat of a mystery. Experiments with CeO₂ suggest that the origin may be due to vacuum fluctuations.

Rogue waves have been observed in fluids and other wave contexts. Experiments now show the formation of 3D acoustic rogue waves in dusty plasmas; they result from wave–particle interactions driving the dust particles into high-amplitude dynamics.

Single carbon vacancies in graphene can host a positive charge that is tunable. When this charge is large enough such vacancies resemble artificial atoms, with an induced sequence of quasi-bound states that trap nearby electrons.

In analogy to fluids, electric currents can exhibit viscosity — albeit with effects difficult to observe experimentally. Now, vorticity is reported as a signature feature of electron viscosity in graphene, which leads to negative nonlocal resistance.

Two intriguing manifestations of Hall physics are reported in a topologically insulating heterostructure: a sign-reversal of the anomalous Hall effect and the emergence of a topological Hall effect.

Amorphous packings of spheres subject to shear and friction jam above a critical density. Simulations now show that shear results in geometrical patterns that are precursors to jammed structures and that friction effectuates the jamming.

Experiments and simulations of the transition to turbulence in fluid flow through a quasi-2D channel reveal critical exponents consistent with directed percolation — long conjectured to be the universality class associated with the transition.

Decades-old speculation that the transition to turbulence belongs to the directed percolation universality class is confirmed with experimental and numerical data for flow through a quasi-one-dimensional Couette geometry.

A magnetotransport study of zirconium pentatelluride now reveals evidence for a chiral magnetic effect, a striking macroscopic manifestation of the quantum and relativistic nature of Weyl semimetals.

A 3D-printed fetal brain undergoes constrained expansion to reproduce the shape of the human cerebral cortex. The soft gels of the model swell in solvent, mimicking cortical growth and revealing the mechanical origin of the brain’s folded geometry.

The relation between structure and dynamics in glasses is not fully understood. A new approach based on machine learning now reveals a correlation between softness—a structural property—and glassy dynamics.

Quantum mechanics sets a fundamental upper limit for the flow of heat. Such quantum-limited heat conduction is now observed over macroscopic distances, extending to a metre, in superconducting transmission lines.

A simulation method connects single-shot measurements in ultracold atom experiments to the probability distribution of the many-body wavefunction, elucidating the role of the fluctuations in different experimental situations.

Fibre networks become rigid at a critical connectivity, but biopolymers giving structure to cells aren’t always well connected. Modelling and experiments on collagen networks show that their rigidity constitutes strain-controlled critical behaviour.

Inelastic Raman scattering is used to probe the critical spin fluctuations in an iron pnictide superconductor, providing insights into the origin of nematic order in this system.