Articles in 2019

Microtubules vary their length by gaining and shedding tubulin dimers dynamically at both ends. But evidence now suggests that dimers may also be incorporated into the middle of the shaft—calling into question existing models of growth dynamics.

The long spin lifetimes observed in polymeric semiconductors hold promise for potential applications. A careful study untangles the main mechanism behind them.

Cells migrating within a collective naturally have restricted access to their surroundings. Experiments on micropatterned substrates now show that this confinement can regulate epithelial migration—governing cell morphology, forces and velocity.

The principle of gauge invariance in quantum electrodynamics may be violated by approximate models in the presence of strong light–matter interactions. A general approach solves gauge ambiguities and offers a way to construct gauge-invariant Hamiltonians.

A unified theory for the conduction of heat in materials is derived and shown to account for both the limiting regimes of periodic crystals and aperiodic glasses.

Stress relaxation in cell monolayers shows remarkable similarities with that of single cells, suggesting the rheology of epithelial tissues is mediated by the actomyosin cortex—with dynamics reminiscent of those on a cellular level.

Renormalization group calculations incorporate band structure and interaction effects on an equal footing. Applying this methodology to Ge-doped Pb₃Bi shows that this material is a chiral topological superconductor and hosts Majorana fermions.

A study of how migrating cells optimize their search efficiency in the absence of directional cues reveals a self-organizing system that mediates superdiffusive motion—and sheds light on how cells navigate noisy environments.

The structural integrity of a cell’s nucleus is maintained by a polymer network known as the nuclear lamina. A simple biophysical theory reveals two regimes by which this network can rupture, depending on the structure of the nuclear envelope.

Machine learning techniques have latterly gained currency in condensed-matter physics, for example by identifying phase transitions. An unsupervised machine learning algorithm that identifies topological order is now demonstrated.

Small-angle neutron scattering experiments of the layered antiferromagnet Ca₃Ru₂O₇ reveal a metamagnetic spin texture that is indicative of an extraordinary coexistence of spin orders belonging to different symmetries.

Droplet sequences in microfluidic networks are shown to form trains that oscillate between branches of the network. Control of this effect suggests a mechanism by which red blood cells might avoid certain pathologies by minimizing oscillations.

Following a closed evolution in the Hilbert space, the state vector of a quantum system accumulates a geometric phase factor. A series of weak measurements reveal the origin of this in the back-action of any quantum measurement.

When a wound heals, different types of branched and bundled actin structure form, each designed to perform a specific function. Experiments and theory now suggest that the actin architecture depends on the stiffness of the cell’s surroundings.

A phase transition often implies symmetry breaking in the system. However, an unconventional first-order phase transition is predicted, where higher-order symmetry than that of the underlying Hamiltonian emerges exactly at the phase boundary.

High-resolution experiments attribute surprisingly large forces to the molecular motors helping a cell sense its surroundings. A two-state theory interprets the contractile properties of these motors as emergent features of their collective behaviour.

A bottom-up mathematical approach provides a framework for the design of mechanical networks of two- or three-dimensional frames composed of freely rotating rods and springs that achieve any desired coordinate motion.

Simulations of a system comprising polymer rings with internal elasticity reveal a key role for deformation in controlling the microscopic dynamics of soft colloids.

Getting a picture of a d or f atomic orbital has been a challenge, but the X-ray scattering technique reported here enables direct transition from core s orbitals to the d orbitals so that their spatial shape can be mapped with no need for modelling.

Bacteria swimming near surfaces can get trapped in circular trajectories that lead nowhere, hindering efficient surface exploration. A harmful strain of bacteria is now shown to circumvent the problem by exploiting transient surface adhesion events.