Volume 4 Issue 4, April 2008

Beautiful, intricate patterns in limestone result from feedback between hydrodynamics and chemistry. This self-organizing process resides in an unfamiliar region of parameter space for systems of deposition under fluid flow.

Despite more than a decade of study, single-wall carbon nanotubes still have the ability to surprise. One recent study finds that in ultraclean nanotubes an unexpectedly strong spin–orbit coupling arises; another demonstrates their ability to support one-dimensional Wigner crystals.

Quantum mechanics provides the means for solving certain communication tasks more efficiently than is possible classically. Photons entangled in multiple degrees of freedom could provide a route to fully tap that potential.

In a solid, electrons behave differently than in a vacuum. In particular, their charge can break up into fractions of the elementary charge. Theoretical work shows how the electron's spin could help to observe fractional charges directly.

The complex behaviour of high-temperature superconductors has inspired some complex models and theories, but a conventional model seems to work just fine for scanning tunnelling spectroscopy.

Quantum spin Hall insulators are new states of matter that were recently predicted and observed. A theoretical work now explores distinct experimental manifestations resulting from the exotic behaviour that characterizes these structures.

An experimental study of a ‘dimeric’ single-molecule magnet—consisting of two coupled half-wheels of spin 7/2 each—provides evidence for quantum interference between the two sub-systems.

Classically, one photon can transport one bit of information. But more is possible when quantum entanglement comes into play, and a record ‘channel capacity’ of 1.63 bits per photon has now been demonstrated, using a method that overcomes fundamental limitations of earlier approaches to ‘superdense coding’.

High-temperature superconductors are difficult to model because most conventional theories fail for the strong repulsive interactions between electrons. But what if the correlations are not as strong as believed? Perhaps the magnetic correlations are more essential.

Arrays of quantum dots can be useful for building ‘artificial molecules’, and potentially as elements of quantum information networks. But in practice, no two dots are the same. An optical technique provides the means for in situ characterization of individual dots, and their collective properties.

Seeding a free-electron laser with pulses from a high-harmonic UV-light source increases its output intensity by three orders of magnitude. This approach has the potential to generate temporally coherent light at wavelengths down to the all-important ‘water window’, vital for studying biological samples.

A comprehensive survey of data from the Galileo spacecraft suggests that the principle mechanism of ultra-relativistic electron acceleration in Jupiter’s magnetosphere arises from their gyro-resonant interaction with whistler waves, in contrast with conventional understanding.

Unlike most rocks, calcium carbonate at geothermal hotsprings grows at a visible rate, thus enabling a comparison between time-lapse photography, mathematical models and simulations of the growth dynamics.

The one-dimensional case of the so-called ‘Wigner crystal’ phase of electrons—long predicted but previously only seen in two-dimensional electron systems—has finally been observed, in a carbon nanotube.

In conventional superconductors, the critical temperature goes to zero as the density of charge carriers falls due to increased scattering. But in high-temperature superconductors, the scattering rate as a function of charge carriers was unknown, until now.

Froths and foams are complex structures, particularly those that disappear irreversibly. Superconducting froth, however, can be reversibly controlled by several external parameters, so it may help quantify froth dynamics across different systems.

A little foresight.