Volume 11 Issue 5, May 2012

Progress in controlling different ferroic orders such as ferromagnetism and ferroelectricity on the nanoscale could offer unprecedented possibilities for electronic applications.

A dendritic polymer consisting of inversely oriented lipid head groups on a polyvalent polyglycerol scaffold makes an effective reversible biomembrane adhesive that may find use as a tissue sealant and a drug-delivery vehicle.

Accurate and extensive measurements of the compositional dependence of the Curie temperature brings us one step closer to solving the puzzle of the origin of ferromagnetism in the model ferromagnetic semiconductor (Ga,Mn)As.

Evidence of a transition between two coexisting liquids of the same composition in a water–glycerol mixture, where glycerol prevents the crystallization of water, provides a unique link to an elusive liquid–liquid transition in pure water.

The ability of spintronics to re-energize itself in directions that germinate new subfields has made it one of the most fertile grounds for basic research aimed at future applications. A brief overview of the connections between five emerging subfields suggests exciting things to come.

Spin-transfer torque is the rotation that a spin-polarized current induces on the magnetization of the solid it flows through. The way in which currents generate torques in a wide variety of magnetic materials and structures is discussed in this Review, as well as recent state-of-the-art demonstrations of current-induced-torque devices that show great promise for enhancing the functionality of semiconductor devices.

The spin Hall effect is a relativistic spin–orbit coupling phenomenon, which can be used to electrically generate or detect spin currents in non-magnetic systems. This Review discusses the experiments that have established the basic physical understanding of the effect, and the role that several of the spin Hall devices have had in the demonstration of spintronic functionalities and physical phenomena.

Spin caloritronics focuses on the interaction of electron spins with heat currents. This Review describes newly discovered physical effects that have re-invigorated the field by stimulating further research into understanding the fundamentals of spin–phonon interactions, and providing new avenues to explore to improve current thermoelectric technology.

Control of the electron spin as well as its charge is predicted to lead to efficient electronic devices, with potentially new functionalities. Injecting and manipulating spin-polarized carriers in silicon is a natural step towards integrating spintronics with current technology. This Review describes the first encouraging results as well as the open questions and challenges that still remain.

Graphene and topological insulator two-dimensional electron systems are described by massless Dirac equations. Although the two systems have similar Hamiltonians, they are polar opposites in terms of spin–orbit coupling strength. The status of efforts to achieve long spin-relaxation times in weakly spin–orbit-coupled graphene, and large current-induced spin-polarizations in strongly spin–orbit-coupled topological insulator surface states are reviewed in this Progress Article.

The observation of a superconductive current flowing through a topological insulator is considered the first step towards the observation of the elusive Majorana fermions. This is now achieved in a superconductor/topological insulator/superconductor junction in which direct evidence of Josephson supercurrents is reported.

A common route to obtain efficient thermoelectrics is to optimize the ratio between electrical and thermal conductivity. Typically, materials with a complex, glass-like phonon structure and therefore a very low thermal conductivity are studied. Now, a route showing that solid ions in a liquid-like state can have a low enough thermal conductivity to compete with the best existing thermoelectrics is proposed.

Electromagnetic waves propagating on the surface of materials are used in a variety of applications such as on-chip photonics. The demonstration now of a nearly 100% efficient coupling of these surface waves to freely propagating waves promises to improve photonic applications such as surface–plasmon couplers, antireflection coatings and many more.

The maximum imaging resolution in classical optics is limited to approximately the wavelength of light used, and subwavelength resolution can only be achieved by advanced imaging schemes. The appeal of the super-oscillatory lens optical microscope described here is that it enables subwavelength imaging with, in principle, unlimited resolution using a modified conventional microscope.

The plausible existence of a liquid–liquid transition (LLT) pre-empted by crystallization in supercooled water has long been debated. So far, indications of such a ‘hidden’ LLT have been found in nanoconfined water and in the amorphous polymorphism of ice. Now, the finding of an isocompositional LLT in a water–glycerol mixture where glycerol prevents water crystallization suggests a new link to an elusive LLT in pure water.

Although (Ga,Mn)As is considered the model ferromagnetic semiconductor, the electronic structure of the charges — holes in this case — and its connection with the Curie temperature (T_C) are still unclear. Experiments now provide a direct link between T_C and the existence of an impurity band for the holes. Clarifying this issue is essential to designing other materials with potentially higher T_C.

Metamaterials have enabled many different photonic technologies. Now, the realization of holographic information storage promises new types of applications, in particular when combined with other metamaterials functionality.

Coherent diffractive imaging is a powerful numerical technique that can reconstruct and enhance images. The demonstration of this technique with subwavelength resolution now exhibits the possibility of new applications such as single-shot imaging of ultrafast events with ultrahigh resolution.

Although materials used in electrochemical devices for energy applications would benefit from the precise structural control that can be achieved by using silica sol–gel chemistry, such synthetic approaches typically result in insulating porous materials. Now, a simple approach based on a multifunctional sol–gel precursor allows the synthesis of porous nanocomposites with metallic percolation networks exhibiting high electrical conductivity.

The headgroup of phospholipids in eukaryotic cell membranes contains phosphatidyl choline (PC). Now, branched polyglycerols decorated with the 'PC-inverse' choline phosphate (CP) are shown to behave as 'universal' biomembrane adhesives, binding electrostatically to cell membranes and to PC-containing liposomes. Binding can be reversed by exposure to PC-containing polymers. These adhesives may find use as tissue sealants and as drug-delivery vehicles.

Spintronics studies the properties of the electron spin, with a view to improving the efficiency of electronic devices and to enrich them with new functionalities. This Nature MaterialsInsight provides a compact, yet comprehensive overview of a selection of topics that have rapidly developed in the past few years.