Research articles

Chemical substitution often mimics the effects of applied pressure on a compound, and ‘doping’ is a standard way to reach a quantum critical point from a given phase. However, CeCoIn₅ is a natural quantum critical superconductor, and Cd-doping tunes the system away from criticality. Applied pressure reverses the effect of doping, but although superconductivity is restored, quantum criticality is not.

Double quantum dots are proving themselves to be an excellent test bed for many-body physics. These artificial atoms now demonstrate a phenomenon in which the capacitive coupling between them causes the spin and charge degrees of freedom of the electrons in the system to become entangled—the so-called SU(4) Kondo effect.

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.

CeCoIn₅ is a d-wave heavy-fermion superconductor. By tuning the coupling between magnetic and superconducting order, a phase with inhomogeneous p-wave superconductivity can be detected, which coexists with d-wave superconductivity and spin-density-wave order.

The creation of Feshbach molecules by exploiting engineered spin–orbit coupling in a spin-polarized Fermi gas advances the experimental study of topological superfluidity in ultracold gases.

In open quantum systems the correlations between the system and its environment play an important role. A trapped-ion experiment demonstrates that these correlations can be detected without accessing or knowing anything about the environment or its interactions.

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.

Defects in silicon carbide can produce continuous-wave microwaves at room temperature. Spectroscopic analysis indicates a photoinduced inversion of the population in the spin ground states, which makes the defects a potential route to stimulated amplification of microwave radiation.

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.

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.

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.

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.

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.

Confined within a porous aerogel, superfluid ³He loses its long-range order owing to random microscopic disorder, and becomes a glassy superfluid. Intriguingly, this effect can be switched off and the superfluidity restored.

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.

A room-temperature motion sensor with record sensitivity is created using a levitating silica nanoparticle. Feedback cooling to reduce the noise arising from Brownian motion enables a detector that is perhaps even sensitive enough to detect non-Newtonian gravity-like forces.

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.

A high-confinement plasma that is potentially useful for controlled fusion has now been sustained for over 30 s. The Experimental Advanced Superconducting Tokamak in Hefei, China, achieved this record pulse length by first confining the plasma using lithium-treated vessel walls, and then maintaining it with a so-called lower hybrid current drive.

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.