Articles in 2013

A quantum gas trapped in an optical lattice of triangular symmetry can now be driven from a paramagnetic to an antiferromagnetic state by a tunable artificial magnetic field.

Networks of networks are vulnerable: a failure in one sub-network can bring the rest crashing down. Previous simulations have suggested that randomly positioned networks might offer some limited robustness under certain circumstances. Analysis now shows, however, that real-world interdependent networks, where nodes are positioned according to geographical constraints, might not be so resilient.

Strongly interacting condensed-matter systems are often computationally intractable. By introducing a periodic lattice to a holographic model developed by string theorists, it becomes possible to study anisotropic materials that are insulating in certain directions but conducting in others.

A study of an actomyosin active gel now demonstrates the importance of the crosslinking density of actin polymers in enabling myosin motors to internally drive contraction and rupture the network into clusters. These results could help us to better understand the role of the cytoskeleton in cell division and tissue morphogenesis.

Experimentally verifying that quantum states are indeed entangled is not always straightforward. With the recently proposed device-independent entanglement witnesses, genuine multiparticle entanglement of six ions has now been demonstrated.

Charge noise and spin noise lead to decoherence of the state of a quantum dot. A fast spectroscopic technique based on resonance fluorescence can distinguish between these two deleterious effects, enabling a better understanding of how to minimize their influence.

A Wigner molecule—a localized pair of interacting electrons—is now created in a carbon nanotube. The high-quality, electronically pristine tubes enable a full characterization of the energy spectrum, laying the groundwork for future studies of interacting fermion systems in one and two dimensions.

A magnetic field can lift the spin degeneracy of electrons. This Zeeman effect is an important route to generating the spin polarization required for spintronics. It is now shown that such polarization can also be achieved without the need for magnetism. The unique crystal symmetry of tungsten selenide creates a Zeeman-like effect when a monolayer of the material is exposed to an external electric field.

In topological insulators, studies have largely concentrated on the spin part of the wavefunction. But the spin–orbit coupling is strong, so the orbital components of the wavefunction need to be measured as well. Surprisingly, the orbital wavefunction turns out to be asymmetric about the Dirac point.

Neuronal networks can spontaneously exhibit periodic bursts of collective activity. High-resolution calcium imaging and computer modelling of in vitro cultures now reveal that this behaviour is a consequence of noise focusing—an implosive concentration of spontaneous activity due to the interplay between network topology and intrinsic neuronal dynamics.

The modelling of plasmonic systems is complicated by the broad range of length scales involved: the physical dimensions of the structure might be as small as 1 nm, whereas the wavelength of the light involved can be a few hundred nanometres. It is now shown that transformation optics, a technique successfully used to design metamaterials, is also valuable for circumventing these problems.

When a domain wall of a given chirality is injected into a magnetic nanowire, its trajectory through a branched network of Y-shaped nanowire junctions—such as a honeycomb lattice, for instance—can be pre-determined. This property has implications for data storage and processing.

Atom and ion trapping provides new tools for ultracold chemistry. Using these techniques it is possible to measure the population distribution of the product states of three-body recombination in an ultracold atomic gas.

Magnetic excitations, or spinons, in a quasi-one-dimensional quantum magnet are investigated in an inelastic neutron-scattering experiment. The measurements confirm the existence of theoretically predicted higher-order spinons.

A pulsar is a rotating neutron star that beams out electromagnetic waves. The absence of isolated X-ray pulsars with periods longer than 12 s could be a clue to the structural composition of a neutron star’s crust, as simulations show that an amorphous layer would prevent a pulsar from spinning down.

Near a quantum critical point there are strong critical fluctuations that destroy standard metallic behaviour. Calculations now show that a pseudogap state can arise in the vicinity of an antiferromagnetic quantum critical point, which might be relevant to the cuprate superconductors.

Dynamical maps are well known in the context of classical nonlinear dynamics and chaos theory. A trapped-ion quantum simulator can be used to study the generalized version of dynamical maps for many-body dissipative quantum systems.

Artificial spin-ice promises a means of probing dynamics in frustrated systems, but samples typically only shift between low-lying energy states under an external field. Exploring the energy landscape is now possible, through exquisite control over the thermal fluctuations of mesoscopic magnetic dipoles.

Despite its impressive mechanical and electronic properties, graphene’s magnetic characteristics are poor. However, adsorbed organic molecules can give the material magnetic functionality, and the magnetic moment remains when the molecules combine to form dimers or even a continuous monolayer.

A crystal is a band insulator if the energy bands are filled with electrons. Partially filled bands result in a metal, or sometimes a Mott insulator when interactions are strong. A study now shows that for many crystalline structures, the Mott insulator is the only possible insulating state, even for filled bands.