Volume 13 Issue 7, July 2014

Enhancing the temperature at which superconductivity is observed is a long-standing objective for materials scientists. Recent tantalizing experiments suggest a possible route for achieving this.

In contrast to the ultralow friction that exists between carbon layers in multiwalled carbon nanotubes, multiwalled boron nitride nanotubes are found to exhibit ultrahigh interlayer friction as a result of their ionic character.

By embedding organic dyes in a suitably designed optical microcavity it is possible to strongly mix light and matter excitations, forming states known as microcavity polaritons. These hybrid light–matter states are used to demonstrate energy transfer between organic molecules over long distances.

Computer simulations show that cubic and hexagonal ices nucleate through the formation of a tetragonal metastable ice phase.

X-ray scattering measurements of liquid water down to temperatures at which it spontaneously converts to ice show no signs of the much debated transition from high-density to low-density structural order.

Simulations of a well-studied model of water provide strong support for the coexistence of two distinct metastable liquid-water phases, a long-debated possibility that experiments on supercooled water at negative pressures may be able to confirm.

A state of matter known as a three-dimensional Dirac semimetal has latterly garnered significant theoretical and experimental attention. Using angle-resolved photoelectron spectroscopy, it is shown that Cd₃As₂ is an experimental realization of a three-dimensional Dirac semimetal that is stable at ambient conditions.

Cerium hexaboride is a canonical heavy-fermion system that has come under scrutiny because of its so-called hidden order phase. Now, detailed inelastic neutron scattering experiments reveal an intense ferromagnetic mode, thus overturning the generally accepted view that antiferromagnetic interactions dominate the low-temperature behaviour of this system.

Carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) have similar surface crystallography and mechanical properties. It is now shown that the interlayer sliding friction in multilayer CNTs and BNNTs is, however, different: whereas the telescopic sliding of semi-metallic multiwalled CNTs is known to be vanishingly small, multiwalled insulating BNNTs exhibit ultrahigh interlayer friction that is proportional to the contact area—a result ascribed to the ionic character of boron nitride.

Block copolymers can self-assemble into nanostructures that simultaneously facilitate ion transport and provide mechanical stability. Highly asymmetric charge cohesion effects are now shown to induce the formation of nanostructures with percolated phases desired for ion transport. This strategy could lead to the design of enhanced battery electrolyte materials.

Heterostructures consisting of ferromagnets and heavy metals have become a focus of interest because their strong spin–orbit coupling allows for efficient current-induced magnetization switching phenomena. Now, a magnetically doped topological insulator bilayer is shown to display a range of appealing characteristics for current-induced magnetization switching, including a significantly enhanced efficiency.

Mode-selective vibrational excitations can be used to transiently induce a range of phenomena in strongly correlated states of matter. It is now shown that by exciting apical oxygen distortions in the cuprate system YBa₂Cu₃O_6.5, an unusual photoconductive effect is induced both at low and at high temperatures.

The energy interaction between different exciton species is affected by the optical environment in which they are embedded. It is now shown that mixed exciton–polariton states in strongly coupled microcavities can facilitate energy transfer between organic dyes at length scales greater than the Förster transfer radius.

Disordered photonic materials have the ability to control the flow of light through random multiple scattering. This has the drawback of randomizing both the direction and phase of the propagating light. Now, confined and interacting light modes are demonstrated for a two-dimensional disordered photonic structure.

Perovskite oxides have attracted significant attention as energy conversion materials owing to their unique physical and electronic properties. Anion-based intercalation pseudocapacitance as well as oxygen intercalation in a nanostructured lanthanum-based perovskite (LaMnO₃) have now been exploited for fast energy storage.

At sufficiently low temperature, liquid water crystallizes into ices with cubic or hexagonal symmetry. A simulation study now shows that the nucleation of water into atomic stackings of cubic and hexagonal ices occurs through a metastable precursor phase with tetragonal symmetry, and that this scenario provides an explanation for the unusual pressure dependence of water’s homogeneous crystal-nucleation temperature.

The fracture behaviour of micro- and macroscale bone is shown to be different. In situ micropillar compression experiments on ovine bone demonstrate that microscale lamellar bone is strong and ductile, and shows no damage, whereas on the macroscale, bone shows little ductility and fails in a quasi-brittle manner.

Enzymes involved in copper metabolism and residing within bacterial outer layers are used to polymerize monomers bound to the bacterial cell surface. The composition of the polymers is affected by templating processes and hence the polymers are specific binding agents for the bacteria on which they are grown.

Despite decades of research efforts and debate, a full understanding of the origin of the anomalous properties of liquid water, in particular when supercooled, is not yet in sight. This focus issue highlights the most significant recent findings on this topic.