Volume 5 Issue 9, September 2009

'Fun' science may grab summer headlines, but only the real thing has a lasting effect.

In his short career, Ettore Majorana made several profound contributions. One of them, his concept of 'Majorana fermions' — particles that are their own antiparticle — is finding ever wider relevance in modern physics.

Whether the magnetic response of the copper oxide high-temperature superconductors is governed by itinerant quasiparticles or localized electrons is a hotly debated question. Evidence for the latter suggests an intricate connection to the parent Mott insulator.

Rain hits the ground in drops of different sizes, but the mechanism that produces this distribution is unclear. Could it be that all we need to know is contained in the death of a single drop?

The nature of the 'hidden order' in URu₂Si₂ has resisted characterization for the past twenty-five years. Recent photoemission results report the observation of a narrow heavy-fermion band that sharpens below the mysterious transition and provides new clues about its origins.

Incorporating structural features into random-graph calculations should bring theoretical models describing the properties and behaviour of complex networks closer to real-world systems.

An optical analysis reveals that the electronic correlations in the 'parent' compounds of the iron pnictide superconductors are sufficiently strong to significantly impede the mobility of the electrons.

The conventional photovoltaic effect has now been given a spin twist, enabling spin control in a non-magnetic structure. This concept could yield new methods of detecting and tailoring spin-dependent phenomena in semiconductors.

In quantum information science, dissipation is commonly viewed as an adverse effect that destroys information through decoherence. But theoretical work shows that dissipation can be used to drive quantum systems to a desired state, and therefore might serve as a resource in quantum computations.

URu₂Si₂ is full of mystery. Despite having f-electrons, it is unclear whether heavy electrons are present in the ‘hidden order’ phase. Thanks to photoemission studies, itinerant heavy electrons have been observed just above the hidden-order phase transition, below which the electronic energy spectrum develops a gap.

A systematic neutron-scattering study of large near-optimally doped single crystals of the cuprate superconductor, Bi₂Sr₂CaCu₂O_8+δ, indicates that its magnetic properties are governed by localized magnetic moments, and not by itinerant quasiparticles, as widely expected.

When electrons experience Coulomb repulsion, their kinetic energy becomes significantly reduced. This effect has now been measured in the pnictide superconductor LaFePO, and shows that correlations between electrons in these materials are just as strong as in some copper oxide and ruthenate superconductors.

A two-dimensional lattice of vortices melts into an isotropic liquid with increasing temperature. A microscopic view of the melting transition reveals that this actually occurs in three steps, one of which is an unusual liquid-crystal-like vortex phase.

The magnetization of a magnetic random-access memory is usually controlled by the injection of an externally polarized spin-current. A proof-of-principle demonstration shows that this could instead be manipulated with local fields generated by spin–orbit interactions of an unpolarized current.

Operating a superconducting single-electron transistor near a double Cooper-pair resonance allows it to achieve a charge-detection sensitivity of just 3.6 times the ultimate quantum limit.

Electromagnetically induced transparency in an atomic gas can slow the propagation of images. It is now shown that the diffraction of such images as they propagate can be controlled and even eliminated. This is achieved by using atomic diffusion to influence the spreading of the image.

The effect of disorder in conventional two-dimensional electron systems is usually described in terms of individual electrons interacting with an underlying disorder potential. Scanning single-electron transistor measurements of graphene in a strong magnetic field indicate that in this system, coulombic interactions between electrons must also be taken into account.

A technique that allows the electrical detection of spin-polarized transport in semiconductors without disturbing the spin-polarized current or using magnetic elements has now been demonstrated. The approach could lead to the integration of spintronics elements into semiconductor microelectronic circuits.

Pumping an atomic system with light at a wavelength that is longer than its resonance can lead to cooling. Conversely, it is now shown that pumping with shorter-wavelength light can lead to the stimulated emission of phonons—in analogy to the amplification of photons in lasers.

Black holes are difficult to study experimentally, owing to their distance from us and indeed their very nature. A theoretical study suggests that optical metamaterials that exhibit behaviour that is reminiscent of that of black holes, could enable us to learn more about these and other astrophysical objects.

The first experimental demonstration of saturable absorption in core-electron transitions in aluminium paves the way for investigating warm dense matter, which potentially has an important role in planetary science and the realization of inertial confinement fusion.

The size-distribution profile of raindrops when they reach the ground was previously thought to be governed by complex interactions between neighbouring droplets as they fall. High-speed videos of falling water droplets suggest this is not the case, and that their size distribution can be explained by the fragmentation of individual droplets alone.