Volume 6 Issue 2, February 2010

Quantum theory states that all objects possesses both particle and wave properties. An observation of the 'whispering gallery' modes of a curved surface shows that neutrons are no exception.

How thin can superconducting materials be and still retain their superconductivity? A recent study of thin films grown on silicon substrates reveals that one atomic layer is the limit.

Radiation damage to living tissues occurs not only by the high-energy incident particles of this radiation but also by low-energy secondary electrons that they produce. Two studies now demonstrate that a large fraction of these electrons are generated by a relatively unusual autoionization process known as intermolecular Coulombic decay.

Stars form from gas both dense enough to collapse but diffuse enough to cool into molecules. If cooling is prohibited, a supermassive black hole may form instead. The transition may explain key mysteries of galactic structure.

In recent years, progress has been made towards using cold atomic gases to study the role of disorder in many-body systems. This line of research might offer the key to solving open questions in solid-state physics, but should also provide a new outlook on disordered systems in its own right.

During galaxy formation, the condensing matter can swirl into a new star or feed a central black hole. But what favours one mechanism over the other? It may be that there exist two critical surface densities of the matter cloud: a lower limit above which star formation occurs, and a higher threshold above which black holes form.

High-temperature superconductivity in the cuprates arises when charge carriers are added to an insulator. Between these states lies the so-called nodal liquid at low temperature. Photoemission spectroscopy suggests that superconductivity evolves smoothly from this nodal-liquid state.

There are many two-dimensional superconductors, but only now have monolayers of metallic atoms shown superconductivity. Grown on silicon substrates, epitaxial films of lead and indium represent the thinnest superconductors possible.

When a Van Hove singularity exists near the Fermi energy of a solid’s density of states, it can cause a variety of exotic phenomena to emerge. Scanning tunnelling microscope measurements indicate that when graphite’s graphene sheets are rotated out of their usual alignment, it can generate low-energy Van Hove singularities for which the position is controlled by the angle of rotation.

A structure that allows neutrons to be trapped in long-lived ‘whispering gallery’ states provides scientists with a potentially useful tool to study the interaction of neutrons with matter. It could also allow the development of quantum neutron optics.

Guided by a general framework for wavefront engineering, experiments demonstrate that in a light field, lines of zero intensity can be shaped into knotted and linked loops of arbitrary topology.

X-ray sources such as free-electron lasers offer the potential to study matter at unprecedented spatial and temporal resolution. But that potential is limited by the poor quality of conventional X-ray optical elements. An in situ technique that corrects for wavefront aberrations and allows X-rays to be focused to a spot just 7 nm wide could provide a solution.

It is now shown that the semiconductor InSb becomes transparent to terahertz radiation when an appropriate magnetic field is applied. This effect has never been seen before, despite decades of research on InSb, and the phenomenon could find important applications in the burgeoning field of terahertz imaging.

A long-standing goal of experiments using cold atoms in optical lattices is to simulate the behaviour of strongly correlated electrons in solid-state systems. However, in these experiments, the atoms are confined to spatially inhomogeneous traps, whereas the desired information concerns homogeneous bulk systems. Theoretical work now proposes a way to connect the two types of system.

Measurements of the local response and noise during the ageing of a polymer film show deviations from the expected fluctuation–dissipation theorem. Moreover, scaling behaviour suggests a separate universality class for fragile glass formers.

Analysis of the electrons ionized from water dimers suggests that the energy absorbed by one molecule is rapidly transmitted to the second molecule from which the electron is ejected. This process, referred to as intermolecular Coulombic decay, is a qualitatively different source of low-energy electrons to conventional direct ionization processes.

Most of the low-energy electrons emitted from a material when it is subjected to ionization radiation are believed to be directly ionized secondary electrons. Coincidence measurements of the electrons ejected from water clusters suggests many are produced by a quantitatively new mechanism, known as intermolecular Coulombic decay.