Volume 11 Issue 7, July 2012

System-level planning of theoretical and experimental efforts is increasingly important for the development of modern materials science.

Proposed mechanical metamaterials that contract under tension and expand on compression represent a new approach to realize mechanical properties yet unknown in nature that could lead to applications in microelectromechanical systems.

Experiments with superconductor–graphene hybrids, a novel platform to study quantum phase transitions, suggest that in the proximity of the critical point between superconducting and insulating phases, inhomogeneity emerges at large scales even in apparently uniform disordered systems.

The spreading and differentiation of stem cells depends on the stiffness of the extracellular matrix. Now, experiments on human epidermal and mesenchymal stem cells cultured on substrates with covalently attached collagen fibres show that the cells sense and respond to the anchoring of the collagen fibres to the substrate.

Enzyme-modified plasmonic nanoparticles that generate a signal that is larger when the concentration of the target molecule is lower can detect ultralow levels of the cancer biomarker prostate-specific antigen in whole serum.

Metamaterials have a tremendous potential for applications from biophotonics to optical circuits, although progress has been hampered by intrinsic metal losses. This Review discusses the progress in countering such losses through the use of gain media to realize devices such as nanoplasmonic lasers or improved metamaterials for imaging and nonlinear optical applications.

The so-called pseudogap is a feature of high-T_c superconductors that has puzzled scientists since its discovery. It is of widespread opinion that this feature is associated with a structural symmetry breaking. Now, a highly sensitive scanning tunnelling microscopy experiment shows that a specific structural symmetry is not, as many believed, at the origin of the pseudogap state.

Although intrinsic superconductivity in graphene has not been demonstrated yet, superconductivity in this material can be induced by the proximity effect. The deposition of metallic nanoparticles on a graphene layer allows the status of graphene to be tuned from insulating to superconducting. This metal–graphene hybrid material can therefore be seen as a model system to elucidate the properties of inhomogeneous superconductors.

Light absorption across the bandgap in semiconductors is exploited in many important applications such as photovoltaics, light-emitting diodes and photocatalytic conversion, but whether coloured metals can be used in such applications is unclear. A red metallic oxide Sr_1-xNbO₃ is now shown to be effective under visible light to photocatalyse the oxidation of methylene blue, and the oxidation and reduction of water.

Liquid-crystalline order can be templated in a material by refilling a photopolymerized liquid-crystal cast with the material after the non-polymerized portion has been washed out. This approach has now been used to template, in achiral liquid crystals, chiral three-dimensional blue phases with unprecedented thermal stability that are suitable for narrowband mirrorless lasing and switchable electro-optic devices.

Conventional sensors generate a signal that is directly proportional to the concentration of the target molecule. Now, by means of an enzyme that controls the growth of silver nanocrystals on plasmonic transducers, a nanosensor with sensitivity that is inversely proportional to concentration and that can detect ultralow concentrations of the cancer biomarker prostate-specific antigen in whole serum is demonstrated.

Most materials expand along the direction of an external pulling force, but there are no materials that compress instead. The proposal of mechanical metamaterials that show such negative compressibility promises new artificial materials with designed functionalities.

Topological insulators exhibit intriguing electronic properties that originate from protected metallic states on their surface. Experimental studies so far are based on a limited number of materials. A high-throughput approach now shows how to search for topological insulators in a variety of unexplored classes of materials.

Magnetic cooling could be a radically different energy solution that could replace conventional vapour compression refrigeration in the future. It is now shown that a Heusler-type magnetocaloric alloy exhibits a remarkable cooling capability due to the effect of a sharp structural transformation at a specific temperature. The finding may be of relevance beyond Heusler alloys and represents an important step towards the implementation of cooling systems based on magnetocaloric materials.

Elemental barium at high pressure presents many complex crystal structures that have yet to be determined. The most complex of these crystal structures (phase Ba-IVc at 19 GPa) has now been solved and consists of a commensurate host–guest structure with 768 atoms in the basic unit, where the relative alignment of the guest-atom chains can be represented as a two-dimensional pattern with repeating interlocking motifs.

Developing capture materials and processes that reduce the energy required to separate carbon dioxide from flue gas in power plants is an important area of research. A computational approach to rank adsorbents for their performance in carbon dioxide capture and storage is now proposed, which will enable hundreds of thousands of zeolitic structures to be screened.

The spreading and differentiation of stem cells is influenced by the mechanical properties—in particular by the stiffness—of the extracellular matrix. Now, experiments on epidermal stem cells cultured on substrates with a covalently attached collagen coating show that stem cells sense the stiffness of the substrate through the anchoring density of collagen fibres.