Volume 18 Issue 4, April 2022

Scientists have long preferred the simplest possible explanation of their data. More recently, a worrying trend to favour unnecessarily complex interpretations has taken hold.

Encircling a so-called exceptional point in parameter space elicits a topological response in an open system. An experiment now demonstrates topologically robust chiral spin transfer in a sea of ultracold fermions.

The interactions between coupled photonic resonators influence the properties of the whole network. Dissipative coupling extends the ability to engineer photonic networks and brings fully controllable, ‘utopian’ networks within reach.

The origin of a well-known feature in relaxation data seen in many glass-forming materials has now — possibly — been resolved by means of computer simulations.

Optical control of material properties is usually limited to the region that absorbs the light. Coupling to lattice vibrations that travel close to the speed of light allows ultrafast modulation of polarization deep inside a ferroelectric material.

Hopes for a topological spin liquid phase in ruthenium trichloride have been previously raised by evidence of Majorana modes at the material’s edges. Transport and bulk thermodynamic measurements now strengthen the case for Majorana fermions.

The discovery of charge density waves in a heavily doped cuprate strengthens proposals that these symmetry-breaking modulations play a role in the anomalous electronic properties of high-temperature superconductors.

Drawing on notions from non-equilibrium physics, an interdisciplinary team of economists and scientists describe a framework for understanding the factors that underpin economic resilience, and identify the basic tools for implementing it.

Spin–orbit coupling is an important feature of isolated quantum systems, but less is known about how it responds to dissipation. An experiment in a cold atomic gas now shows how these two effects enable topologically robust spin transfer.

An electron with a linear dispersion relation should contribute half of a quantum of Hall conductance and thereby manifest the parity anomaly. This is demonstrated in a heterostructure of topological insulator materials.

A heterostructure supports the equilibrium bound states of an electron and hole—excitons—that strongly interact with each other. This provides a platform for the quantum simulation of bosonic lattice models.

Earlier measurements of quantized heat transport in the spin liquid candidate α-RuCl₃ agreed with the predictions of Majorana edge modes. Support for this interpretation now comes from the observations of quantization across a large parameter range.

Observation of a high-pressure insulating state in cuprate superconductors provides a fresh challenge for understanding the mechanism of superconductivity in these materials.

Rheological measurements combined with a fully calibrated model show that growth-induced pressure increases macromolecular crowding, inhibiting protein expression and cell growth.

Whether or not an electron wavepacket accumulates a time delay when tunnelling out of an atom is still under debate. Improved all-optical characterization of the tunnelling dynamics by combining one- and two-colour driving fields may shed light on this question.

Visualizing the structural dynamics of isolated molecules would help to understand chemical reactions, but this is difficult for complex structures. Intense femtosecond X-ray pulses allow the full imaging of exploding photoionized molecules, in this case, with eleven atoms.

α-RuCl has a quantum magnetic phase that may be a spin liquid hosting Majorana fermion excitations. Heat capacity measurements show an anisotropic dependence on magnetic-field direction, consistent with predictions for the putative spin liquid.

Soft clamping reduces the dissipation of nanomechanical resonators, but this method has been limited to amorphous materials. When applied in crystalline silicon, it enables resonators with quality factors beyond ten billion.

Topological phenomena have mostly been studied in conservative systems. Experiments on optical resonator networks now show that topologically non-trivial characteristics can also emerge in dissipation.

Topological effects have been found in a range of classical-wave systems, but it was unclear if the concept could be extended to diffusion. An approach using spatiotemporal modulations has now implemented them in a diffusive system

Nonlinear phononics is a method for creating transient structural changes in solids, but its effect is limited to the region of optical excitation. Now, coupling to a propagating polariton allows nonlinear phononics to drive a nonlocal response.

Electrons in an external magnetic field absorb electromagnetic radiation via cyclotron resonance. Deviations from this behaviour in the form of overtone resonances due to ultraslow magnetoplasmonic excitations are now reported for graphene.

The dynamic relaxation spectrum of a supercooled liquid is asymmetric near the glass transition. Overcoming the difficulty of accessing low temperatures and long timescales, simulations now attribute this feature to dynamic facilitation.

A task group recommends values for many constants in fundamental theories of physics and chemistry. Eite Tiesinga and Peter Mohr tell some of the constants’ stories.