Volume 10 Issue 1, January 2014

Promises for UK science must be backed up by long-term plans.

A careful revision of the rudiments of statistical physics shows that negative temperatures are artefacts of Boltzmann's approximate definition of entropy. Gibbs' version, however, forbids negative absolute temperatures and is consistent with thermodynamics.

A combination of two Nobel ideas circumvents the trade-off between power and accuracy in ultraviolet spectroscopy.

Controlled switching of interacting ferroelectric surface domains leads to a variety of regular and chaotic patterns, and could provide a physical platform for performing calculations.

Can a photon be separated from its polarization; or an electron from its magnetic moment? Recent work suggests that in certain contexts, this might not be as impossible as it sounds.

According to classical nucleation theory, a crystal grows from a small nucleus that already bears the symmetry of its end phase — but experiments with colloids now reveal that, from an amorphous precursor, crystallites with different structures can develop.

When the atmospheric surface pressure is just right, a temperature difference can drive a continuous flow of rarefied gas through the soil matrix — a previously unrecognized process on Mars.

Microgravity experiments on a dust bed in a ‘drop tower’ set-up reveal the ability of martian soil to act as an efficient gas pump when heated by the Sun.

Being able to sense nuclear spin dimers is an important next step towards single-molecule structural analysis from NMR measurements. Now the sensing of a single ¹³C–¹³C nuclear spin dimer near a nitrogen–vacancy centre in diamond is reported, together with a structural characterization at atomic-scale resolution.

Magnetic monopoles continue to be elusive. However, an experiment now shows that the interaction of an electron beam with the tip of a nanoscopically thin magnetic needle—a close approximation to a magnetic monopole field—generates an electron vortex state, as expected for a true magnetic monopole field.

Frequency combs provide a broad series of well-calibrated spectral lines for highly precise metrology and spectroscopy, but this usually involves a trade-off between power and accuracy. A comb created by adjusting the time delay between two optical pulses now enables both. This so-called Ramsey comb could probe fundamental problems such as determining the size of the proton.

Networks that fail can sometimes recover spontaneously—think of traffic jams suddenly easing or people waking from a coma. A model for such recoveries reveals spontaneous ‘phase flipping’ between high-activity and low-activity modes, in analogy with first-order phase transitions near a critical point.

The mathematical connection between isostatic lattices—which are relevant for granular matter, glasses and other ‘soft’ systems—and topological quantum matter is as deep as it is unexpected.

An electron and a hole trapped in the same quantum dot couple together to form an exciton. Conventionally the hole involved is a heavy hole. Light-hole excitons are now observed by applying elastic stress to initially unstrained gallium arsenide-based dots. The quasiparticles are identified by their optical emission signature, and could be used in future quantum technologies.

Inelastic X-ray scattering studies of YBa₂Cu₃O_6.6 reveal strong electron-phonon coupling and an inhomogeneous state made up of charge-density-wave nanodomains, which may explain some anomalous properties of the pseudogap state.

Ferroelectric domain switching on the surface of a lithium niobate thin film can be induced by the tip of a scanning probe microscope, and gives rise to both regular and chaotic spatiotemporal patterns. Moreover, the long-range interactions that govern these phenomena can be tuned by varying temperature, humidity, domain spacing and tip bias.

It is shown that for thermodynamics and statistical physics to be internally consistent, Gibbs’ original—rather than Boltzmann’s widely used—definition of entropy needs to be adopted. Consequently, negative absolute temperatures are strictly forbidden, and cold-atom gases are unlikely to be laboratory analogues to dark energy.

Assemblies of colloidal particles provide a micrometre-scale analogue of atomic and molecular liquids and solids. Now, real-time visualization of the liquid-solid transition in systems of spherical colloids reveals complex pathways involving precursors of hexagonal close-packed, body-centred cubic and face-centred cubic symmetry.