Letters in 2010

The strong dependence of the magnetic properties on the growth conditions in (Ga, Mn)As has created the view that ferromagnetism is associated with an intrinsic inhomogeneity. Muon-spin-relaxation experiments now show that strong and homogeneous ferromagnetism is instead present in both insulating and metallic films.

Several routes designed to induce a bandgap opening in graphene have been proposed. It is now demonstrated that hydrogen adsorption on the Moiré pattern induced by an iridium substrate can induce a bandgap of 450 meV.

The strong coupling of light and matter is responsible for phenomena such as Bose–Einstein condensation. In a study of strong-coupling effects in semiconductor microcavities, the interaction between a two-level electronic system and a light field has now been observed.

Multiferroics are promising for their ability to use an electric polarization to control magnetism and vice versa. However, ferroelastic effects during the switching of multiferroics such as BiFeO₃ destabilize the ferroelectric state. A new approach for the switching of these sorts of compound may now represent a solution to this problem.

While superconductivity experts investigate the fundamental properties of iron pnictides, it is worth wondering whether the properties of these materials are good enough for applications. A strategy for growing high-quality BaFe₂As₂ thin films shows that the use of an appropriate buffer layer allows very high critical currents to be reached.

Resolving the surface structure and chemistry of oxides such as strontium titanate has so far proved difficult. Rings of six or eight corner-sharing TiO₄ tetrahedra and a homologous series of surface reconstructions for SrTiO₃(110) are now predicted.

The use of silicon nanostructures in solar cells offers a number of benefits, such as the fact they can be used on flexible substrates. A silicon wire-array structure, containing reflecting nanoparticles for enhanced absorption, is now shown to achieve 96% peak absorption efficiency, capturing 85% of light with only 1% of the silicon used in comparable commercial cells.

The mechanical properties of many materials are different on the nanoscale than they are in the bulk. In the case of metallic glasses, nanometre-scale samples show enhanced ductility. This tensile ductility has now been quantified for samples with diameters down to 100 nm, where a new regime of increased ductility during deformation is observed.

Creating p–n junctions using semiconducting polymers has proved to be challenging because of difficulties in depositing semiconducting polymer films. Now, by using a cationic conjugated-polymer electrolyte and a neutral conjugated-polymer layer, devices with a fixed bilayer organic p–n junction and fast response times have been fabricated.

In most suspensions viscosity decreases with increasing shear rate. The opposite effect, shear thickening, is a problem for industrial applications. An understanding of how particle interactions in suspensions influence shear thickening may lead to a solution of this problem through the design of smart suspensions.

Electron transport through metal–molecule contacts greatly affects the operation of electronic devices based on organic semiconductors and single-molecule junctions, but the nature of the contact barrier remains poorly understood. Scanning tunnelling microscopy experiments reveal a significant variation on the submolecular scale, leading to a scheme to locally manipulate the potential barrier of the molecular nanocontacts with atomic precision.

Why does the bandgap in semiconducting carbon nanotubes depend on the way it is measured? It is now shown that the results obtained by scanning tunnelling spectroscopy are usually influenced by screening, which creates the discrepancy with optical measurements. The results highlight the importance of many-body effects in the electronic properties of carbon nanotubes.

Control of magnetization in ferromagnetic metals can be achieved through the spin torque of currents of spin-polarized electrons, usually injected externally. It is now shown that even without this spin-polarized injection, a current can induce strong spin torques through the Rashba effect. The efficiency of this process makes it a realistic candidate for room-temperature spintronic applications.

Jamming transitions of disordered systems such as foams, gels and colloidal suspensions, describe the change from a liquid to a solid state. An investigation of the three-dimensional properties of jamming shows how, for example, unjamming occurs simultaneously in all directions even if it is induced in one direction only.