Letters in 2011

Spin-valve structures used in modern hard-drive read heads and magnetic random access memories comprise two ferromagnetic electrodes. It is now shown that antiferromagnets can be used as electrodes in spin valves. The results open a wide range of new possibilities for the choice of materials for spintronics devices.

Producing materials capable of simultaneously absorbing hydrogen and releasing it on-demand is challenging. An air-stable composite material consisting of magnesium nanocrystals embedded in a polymer matrix is now shown to exhibit both high hydrogen-storage density and rapid kinetics.

Knowledge of the symmetry of the superconducting order parameter is essential to understand the origin of superconductivity itself. Studies on the recently discovered heavily doped Fe₂Se₂ now show that in these compounds the order parameter has a relatively simple symmetry compared with most other Fe-based superconductors, questioning again the generality of the results obtained so far.

Because nanotubes are generally prepared from their constituent elements at high temperatures, it is difficult to control their size, shape and electronic states. A bottom-up approach for the room-temperature fabrication of an assembly of infinite square-prism-shaped nanotubes with high tunability, using metal ions and organic molecules as building blocks, is now reported.

Magnetic domain walls can be controlled through a spin torque, which is usually influenced by extrinsic factors, such as defects, that pin the domain walls to specific configurations. It is now shown that intrinsic pinning conditions can be achieved, which will facilitate the development of efficient information storage devices based on domain wall control.

Using boron nitride as a substrate for graphene has been suggested as a promising way to reduce the disorder in graphene caused by space fluctuations. It is now shown by scanning tunnelling microscopy that graphene conforms perfectly to boron nitride and the charge fluctuations are minimal compared with the conventionally used substrate, silica. Boron nitride could really be the natural graphene substrate.

The resolution of electron microscopy has increased through the years, and scientists have been able to measure progressively lighter elements. The ultimate goal has now been reached with the imaging of hydrogen atoms.

The occupation of electronic orbitals on the surface and interface of oxide thin films and heterostructures is a key influence over their properties, including magnetism and superconductivity. A new spectroscopy technique now provides the first quantitative, spatially resolved data of orbital occupation in oxide structures.

Electronic devices based on complex oxides offer the possibility to connect electrical devices with phenomena such as magnetism and superconductivity. However, existing oxide field-effect transistors have drawbacks such as high operation voltage. The demonstration of a metal-base transistor whose geometry makes use of the strong internal electric fields in oxide heterojunctions may now offer a new platform for oxide electronics.

The control over phase transitions in complex oxides offers the possibility to control their electronic and structural properties. The discovery of a new route to ultrafast photoswitching of manganites via high-energy ‘hidden’ excited states offers the possibility of phase transitions free from thermal effects.

Considerable attention has been given in the past few years to two-dimensional electron gases formed at the interface between two bulk insulators. It is now shown that a similar electronic system can be created on the surface of an oxide insulator simply by exposure to UV light.

Is friction dominated by electrons or by lattice vibrations? A nano-contact experiment shows that on a Nb surface friction drops by a factor of three when crossing the superconductivity transition, showing that it has essentially an electronic nature in the metallic state, whereas the phononic contribution dominates in the superconducting state.