Reviews & Analysis

Proposed mechanical metamaterials that contract under tension and expand on compression represent a new approach to realize mechanical properties yet unknown in nature that could lead to applications in microelectromechanical systems.

The spreading and differentiation of stem cells depends on the stiffness of the extracellular matrix. Now, experiments on human epidermal and mesenchymal stem cells cultured on substrates with covalently attached collagen fibres show that the cells sense and respond to the anchoring of the collagen fibres to the substrate.

Enzyme-modified plasmonic nanoparticles that generate a signal that is larger when the concentration of the target molecule is lower can detect ultralow levels of the cancer biomarker prostate-specific antigen in whole serum.

Metamaterials have a tremendous potential for applications from biophotonics to optical circuits, although progress has been hampered by intrinsic metal losses. This Review discusses the progress in countering such losses through the use of gain media to realize devices such as nanoplasmonic lasers or improved metamaterials for imaging and nonlinear optical applications.

To drive the formation of tubular structures, cells remodel their extracellular microenvironment to induce coordinated migration. It is now found that a mechanical feedback loop, involving the interaction of cell traction forces with collagen fibres, facilitates the formation of long epithelial tubules.

Progress in organic electronics depends on our understanding of the structure–property relationships of organic materials. Resonant scattering of polarized soft X-rays by aromatic carbon bonds has now been used to probe molecular orientation in thin organic semiconductor films down to length scales of 20 nm.

Colloidal particles interacting through DNA linkers can be designed to form solids that melt when either heated or cooled. This scenario widens the temperature window in which colloidal superlattices form by reducing kinetic bottlenecks.

Experiments with superconductor–graphene hybrids, a novel platform to study quantum phase transitions, suggest that in the proximity of the critical point between superconducting and insulating phases, inhomogeneity emerges at large scales even in apparently uniform disordered systems.

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.

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.

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.

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.

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.

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.

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.