News & Views in 2011

For an important class of liquids, relaxation dynamics are constrained by a surprisingly simple scaling relationship between density and temperature. It seems that thermodynamics holds the key to pinning down the exponent.

A demonstration of the ability to produce arbitrary-shaped electron bunches from an ultracold gas represents an important step towards studying ultrafast molecular processes in laboratories around the world.

Quantum states of light could be a better probe for materials than classical states, but they are hard to generate in the laboratory. A scheme that combines large amounts of data with sophisticated theoretical analysis gets around this limitation.

Generating intense bursts of high-energy radiation usually requires the construction of large and expensive facilities, such as free-electron lasers, which are based on conventional particle accelerators. Laser-driven accelerators offer a cheaper and smaller alternative, and they are now capable of generating intense bursts of gamma-rays.

Electrons at an interface between two insulating oxides are now shown to exhibit ferromagnetism — a collective electronic state not seen in the bulk of either individual oxide.

A comprehensive map of the spin fluctuations in high-temperature superconductors is emerging through the application of a novel experimental technique — and the surprising results are challenging theorists.

Surfaces inherently lack inversion symmetry. This property is now shown to promote the spontaneous formation of a lattice of spin vortices in a thin magnetic film, a finding that suggests a simple route towards new spintronics applications.

A strictly one-dimensional electron liquid or 'Luttinger liquid' may seem a purely theoretical construct. But measurements of the electronic structure of strings of gold atoms self-aligned on a germanium surface suggest this mythic state of matter is real, offering new possibilities to investigate and ultimately control its properties and behaviour.

In a Mott insulator, repulsive interactions suppress conductivity. Such behaviour has been demonstrated, individually, for both bosonic and fermionic atoms in optical lattices. Now, a Bose–Fermi mixture is found to be Mott insulating too, even when the individual components are not.

The linear and hyperbolic electronic bands of single- and bilayer graphene give rise to quantum Hall effects that are different from those seen in previously studied 2D systems. The electronic structure of trilayer graphene includes both types of band, giving rise to even richer behaviour.

Equilibrium free-energy landscapes supply important information about complex molecules such as nucleic acids and proteins. But can equilibrium landscapes be calculated from measurements on a non-equilibrium system?

A single microwave photon in a superposition of two states of different frequency is now demonstrated using a superconducting quantum interference device to mediate the coupling between two harmonics of a resonator. Such quantum circuits bring closer the possibility of controlling photon–photon interactions at the single-photon level.

To first approximation, the dispersion relation around the Fermi energy of single-layer graphene is linear, making its charge carriers behave like massless relativistic subatomic particles. More careful inspection of its low-energy band structure suggests the picture is more complex, extending the analogy even further.

Phase information can be obtained from inelastically scattered X-rays by combining parametric down-conversion with tunable quantum interference. This is a step towards putting this nonlinear phenomenon to a practical use in the X-ray regime: investigating the optical response of chemical bonds at their electron-volt and subnanometre scales.

Extensive numerical simulations provide evidence that the thermodynamic behaviour of supercooled silicon is similar to that proposed for supercooled water: a line of liquid–liquid transitions that ends at a critical point. In the case of silicon, however, the critical point occurs at negative pressures.