Letters in 2012

Quasicrystals are known for their lack of long-range periodic order. The observation in quasicrystals of quantum critical phenomena that are not seen in their crystalline approximants now demonstrates that the quasicrystals also have unique electronic states.

There are a number of approaches to coupling light with thin-film devices such as solar cells. The demonstration now that multiple scattering processes in two-dimensional random media enable efficient light trapping suggests new possibilities for photon management with the benefit of broad spectral and angular operation.

Understanding the consequences of the interplay of defects and local curvature in crystals is far from complete despite the considerable influence that a defect has on the crystal’s local properties. It is now found that interstitials inserted in curved crystals at oil/glycerol interfaces can fractionate into two dislocations, which glide through the lattice in opposite directions until they get absorbed into existing dislocations, scars or pleats.

The properties of graphene have been widely studied for applications in electronics. Expanding its use in photonics as well, it is now demonstrated that the propagation of terahertz waves can be electronically switched by such a single atomic layer of carbon.

Topological crystalline insulators are a novel state of matter in which the topological features of the electronic structure have been predicted to originate from crystal symmetries. Now an experimental realization of a topological crystalline insulator is reported, in the form of Pb_1−xSn_xSe.

Mechanistic details on how a molecular crystal nucleates on a surface remain limited because it is difficult to probe rare events at the molecular scale. Now, single-molecule real-time transmission electron microscopy shows that a single-molecule template on the surface of carbon nanohorns can nucleate the crystallization of two organic compounds, and that the mechanism is reminiscent of a two-step nucleation process in solution.

Memristors are devices whose dynamic properties are of interest because they can mimic the operation of biological synapses. The demonstration that ferroelectric domains in tunnel junctions behave like memristors suggests new approaches for designing neuromorphic circuits.

Its high carrier mobility is one of the factors that makes graphene interesting for electronic and photonic applications at terahertz frequencies. Such possibilities are now further supported by the demonstration of an efficient room-temperature graphene detector for terahertz radiation that promises to be considerably faster than competing techniques.

Whether a liquid forms a crystal or a glass on solidification depends on many factors. The finding now that a disordered structure is favoured in B₂O₃ because the system cannot choose between several crystalline polymorphs of similar energy highlights a link between glass formation and crystallization.

The dynamics of spins in single atomic layers of cuprates and other compounds are important for understanding their properties, such as magnetism and high-temperature superconductivity. Now, spin excitations in isolated single layers of a cuprate have been measured, providing valuable feedback on their magnetic properties.

The electronic interactions at the interface of oxide materials promise properties that can be very different from those of the parent compounds. The finding that many-body interactions in oxide superlattices can be used to engineer electronic properties offers a new strategy for designing oxide heterostructures.

Multiferroics show simultaneous electrical and magnetic order. The suggestion that ferroelectricity in an organic multiferroic is not driven by the usual atomic displacements but instead by ordering of electronic charges opens the possibility of a new group of multiferroic compounds.

The motion of dislocations under stress is a key process in crystal plasticity. The finding that at low temperatures differences between experiments and theoretical predictions of dislocation activation can be explained by quantum effects arising from crystal zero-point vibrations represents a significant advance in our understanding of plasticity.

Van der Waals interactions are critical to the understanding of functional metal/molecule interfaces in catalysis, molecular electronics and self-assembly. Such interactions have now been characterized at the single-molecule level through a combination of measurements of the stretching mechanics of molecular junctions and atomistic simulations.

Heterostructures of very thin films have been used for decades in research and industry. Now a transmission electron microscopy study demonstrates the possibility of realizing perfect structures built by piling up one-atom-thick layers of graphene and boron nitride.

The interaction between electrons and phonons is important for many materials properties. The finding that phonon modes of a superconducting thin film can influence the properties of an adjacent normal conductor, even over comparatively long distances, suggests new ways of controlling electron–phonon interactions.

Graphene is often referred to as the strongest material in existence. That may be so for a perfect crystal, but most graphene sheets are polycrystalline, and the grain boundaries affect their mechanical properties. A new study reveals that both the density and detailed arrangement of the defects that form the grain boundaries play a significant part in determining the strength of a polycrystalline graphene sheet.

Tissues with perfusable vascular networks can be fabricated through layer-by-layer assembly, bioprinting or sacrificial moulding, but current approaches are slow, have limited resolution, or place significant constraints on the materials or the processing conditions. A rapid and general vascular casting approach using carbohydrate glass as a sacrificial template to generate tissues containing cylindrical networks that can be lined with endothelial cells and perfused with blood under high-pressure pulsatile flow is now reported.

A thin layer of yttrium iron garnet coating on different materials can transform wasted heat into voltage. The process is based on the spin Seebeck effect and could lead to new types of application that make use of omnipresent wasted heat.

Replacing noble metals in heterogeneous catalysts by low-cost and ubiquitous substitutes such as iron is highly desirable especially because it does not bear potential health risks. A low cost and environmentally benign intermetallic compound Al₁₃Fe₄ is now identified as an active and selective semi-hydrogenation catalyst, which could prove to be applicable to a wide range of heterogeneously catalysed reactions.