Research articles

The nonlinear response of a weak electrolyte to an applied electric field is known as the Wien effect. This is now simulated on a lattice Coulomb gas, therefore providing a platform for investigating system-specific corrections to the firmly established theory accounting for it.

The interplay between magnetism and superconductivity in copper oxide superconductors has been a topic of intense research. Now, a systematic resonant inelastic X-ray scattering study of strontium-doped lanthanum cuprate shows that high-energy magnetic excitations persist over a wide doping range.

Although quantitative understanding of nanocrystal phase transformations is important for efficient energy conversion and catalysis, difficulties in directly monitoring nanoscale systems in reactive environments remain. Direct quantification of hydriding transformations in palladium nanocrystals now clearly reveals that the transformation rates are governed by nanocrystal dimensions.

The recent demonstration that highly disordered polymer films can transport charges as effectively as polycrystalline semiconductors has called into question the relationship between structural order and mobility in organic materials. It is now shown that, in high-molecular-weight polymers, efficient charge transport is allowed due to a network of interconnected aggregates that are characterized by short-range order.

The emergence of superconductivity of insulating oxide interfaces has raised a number of intriguing theoretical challenges. Now, the critical temperature of strontium-doped lanthanum cuprate bilayer samples is shown to remain unchanged over a wide doping range, implying that changes in the carrier density cannot be the origin of the enhanced critical temperatures seen with respect to single-phase samples.

The insulator-to-metal transition occurring in magnetite is known as the Verwey transition, and its precise mechanism has recently come under renewed attention. Using pump–probe X-ray diffraction and optical reflectivity techniques, the dynamics of excitations known as trimerons are now examined, revealing the switching limits of this ubiquitous oxide material.

Polyampholyte hydrogels synthesized from the random polymerization of oppositely charged ionic monomers are shown to be mechanically tough and highly viscoelastic. Strong ionic bonds within the gel act as permanent crosslinks and weaker ionic bonds reversibly break and re-form, enhancing the fracture resistance, shock absorbance and self-healing properties of the materials.

As indicated by direct band-structure measurements and calculations, tiny native imperfections in bilayer graphene are sufficient to cause the generation of coexisting massive and massless Dirac fermions. The massless spectrum is robust against strong electric fields and has a closed-arc topology consisting of a unique chiral pseudospin texture.

The relative displacement of conducting molecules influences their electronic coupling and therefore the charge-transport properties of organic thin films. Electron diffraction patterns now reveal the dominant lattice vibrational modes in organic semiconductors with subnanometre precision and help predict the electronic behaviour of these materials.

The catalytic activity of highly dispersed platinum nanoparticles is not yet well understood. Now, a unique approach that allows precise control of both the size and coverage of platinum nanoclusters reveals that particle proximity influences the oxygen reduction rate of these size-selected clusters, especially in terms of mass normalized activity.

Flexible devices mimicking the sensitivity of human skin typically turn pressure stimuli into electronic signals, which must be further processed to be interpreted by the user. By integrating an active matrix of organic light-emitting diodes in these foldable sensors, pressure can now control the brightness of each coloured pixel, enabling the direct visualization and quantification of the applied stimulus.

Contact-angle and spectroscopy experiments on clean supported graphene and graphite show that these surfaces become more hydrophobic as they adsorb airborne hydrocarbons. Furthermore, the water contact angle on these graphitic surfaces decreases if these contaminants are partially removed by both thermal annealing and controlled ultraviolet–ozone treatments, suggesting that graphitic surfaces are more hydrophilic than previously believed.

Heat is a form of energy that is transported from a hot to a cold region, but it is not a notion that is associated with the microscopic measurement of electronic properties. It is now shown that local thermoelectric measurements can be used for imaging structural disorder in graphene, with high sensitivity, on the atomic and nanometre scales, uncovering soliton-like domain-wall line-patterns separating different graphene regions.

Electronic devices usually rely on the charge or spin of electrons to encode information. A less exploited route is to manipulate the valley quantum number of electrons. It is now shown that the generation, macroscopic transport and detection of valley-polarized electrons in bulk diamond can be achieved with a relaxation time of 300 ns at 77 K, forming a basis for valleytronic devices.

The epitaxial growth of large-area single-domain graphene on hexagonal boron nitride by plasma-assisted deposition is now reported. New sets of Dirac points are produced as a result of a trigonal superlattice potential, while Dirac fermion physics near the original Dirac point remain unperturbed. This growth approach could enable band engineering in graphene through epitaxy on different substrates.

Cathodes for Li-ion batteries operate mainly via an insertion–deinsertion redox process involving cationic species but this mechanism does not account for the high capacities displayed by Li-rich layered oxides. The reactivity of high-capacity Li₂Ru_1−ySn_yO₃ materials is now shown to be associated with a reversible redox process related to a reductive coupling mechanism.

Understanding the distribution of internal local strains within zeolites is important for catalytic applications because they can affect the rates of adsorption and diffusion of guest molecules. A ‘triangular’ deformation-field distribution in ZSM-5 zeolites is now observed, showing the presence of a strain within the crystal that arises from the heterogeneous core–shell structure.

A convincing explanation of why mixed phases of anatase and rutile TiO₂ outperform individual polymorphs is lacking. An energetic band alignment of ~0.4 eV is now shown to exist between the two phases with anatase possessing the higher electron affinity. This observation explains the separation of photoexcited charge carriers between phases and could lead to improved photocatalysts.

Efficient evolution of hydrogen via electrocatalysis at low overpotentials is promising for clean energy production. Monolayered nanosheets of chemically exfoliated WS₂ are shown to be efficient catalysts for hydrogen evolution at very low overpotentials. The enhanced catalytic performance is associated with the high concentration of the strained metallic octahedral phase in the exfoliated nanosheets.

Assessing the effect of nanometre-scale structure on charge transport across micrometre-scale distances remains a fundamental challenge for many energy-conversion technologies. By correlating the structure and the charge transport with nanometre resolution across micrometre-scale distances, nanoparticle aggregates responsible for the high photoelectrochemical water-splitting activity of α-Fe₂O₃ electrodes are identified.