Research articles

Samarium hexaboride has recently come under examination as a possible topological insulator. Transport measurements investigating the effects of magnetic impurities on this system uncover characteristics that are consistent with topologically insulating behaviour, and reveal a strongly suppressed bulk conductivity.

Strontium titanate is widely studied for the myriad of phenomena that are known to occur in the vicinity of its surface. It is now shown that light can be used to induce magnetism in oxygen-deficient crystals of SrTiO₃.

The toughness of ceramic materials can be improved by introducing a polymeric or metallic ductile phase, yet most often this is at the expense of strength, stiffness and high-temperature stability. Now, a simple processing route based on widespread ceramic processing techniques is shown to produce bulk ceramics that mimic the structure of natural nacre and have a unique combination of high strength, toughness and stiffness, even at high temperatures.

Biofilms are multifunctional and environmentally responsive assemblies of living and non-living components. By using synthetic gene networks in engineered cells to regulate the production of extracellular amyloid fibrils, and by interfacing the fibrils with inorganic materials such as metal nanoparticles, stimuli-responsive synthetic biofilms with switchable functions and tunable composition and structure have now been produced.

Quantum spin liquids are a state of magnetic order that, in analogy with ordinary liquids, is characterized by fluctuating, disordered spins. By means of specific heat measurements, the frustrated Kondo system Pr₂Ir₂O₇ is shown to undergo a transition to such a state in zero magnetic field.

Optical amplifiers based on erbium ions typically require high pump power densities to produce gain. Now, an organic optical amplifier material composed of erbium ions and a zinc-based organic chromophore is demonstrated to reach population inversion using low-power visible light.

The use of persistent luminescence nanoparticles for in vivo optical imaging commonly requires ex vivo activation before systemic administration, hampering longer-term imaging capabilities. Now, it is shown that near-infrared emitting nanoprobes based on chromium-doped zinc gallate can be activated in vivo using low-energy red light and used for tumour-targeted imaging and cell tracking experiments.

The energy density of supercapacitors can be enhanced by using ionic liquids and electrodes with subnanometre pores, but this tends to reduce their power density. The mechanisms of charging subnanometre pores with ionic liquids are now clarified and molecular simulations suggest that charging of such ionophilic pores is a diffusive process.

Hybrid halide perovskites have demonstrated promising performance as solar cells. It is now reported that these solution-processed materials are also suited to lasing applications, because of the high optical gain and stable amplified spontaneous emission they show in the visible spectral range.

The electronic properties of bismuth under an applied magnetic field have latterly become a topic of interest. An angle-resolved magnetostriction approach is now used to provide thermodynamic evidence for unusual symmetry-breaking effects.

Mechanical cues from the local cellular microenvironment can direct cell fate. Now, experiments with human mesenchymal stem cells cultured on phototunable soft poly(ethylene glycol) hydrogels show that the cells remember past physical environments—with the transcriptional co-activators YAP and TAZ acting as a mechanical rheostat—and therefore that appropriate doses of mechanical cues can be used to manipulate the cells’ fate.

Imparting non-native functions to living plants using nanoparticles opens the possibility of creating synthetic materials that can grow and repair themselves using sunlight, water and carbon dioxide. It is now shown that, both in plant extracts and living leaves, carbon nanotubes traverse and localize within the lipid envelope of plant chloroplasts, enhance their photosynthetic activity, and enable near-infrared fluorescence monitoring of nitric oxide.

Although dispersions of aligned graphene oxide flakes are particularly attractive for electro-optic devices, controlling the alignment of the flakes by using electric fields has proved difficult. It is now shown that the macroscopic alignment of graphene oxide liquid crystals can be controlled through the application of weak electric fields when interflake interactions are sufficiently small, giving rise to the largest Kerr coefficient in a molecular liquid crystal.

In addition to controlling the propagation of light, metamaterials have also received attention for controlling sound. Now, a device that can act as a broadband and omnidirectional acoustic cloak is experimentally demonstrated.

Cuprate superconductors have found limited application for high-field magnets because of difficulties related to grain boundaries. Now, this issue is partially overcome and round wires suitable for magnetic coils are fabricated from Bi₂Sr₂CaCu₂O_8−x.

The collective migration of epithelial cells arises from the interplay between intercellular forces and cellular signalling networks. It is now shown that the migration of an epithelium can be controlled by applying electric fields that bias the signalling networks, and that such galvanotactic control can prompt cell populations to make coordinated U-turns, undergo divergent or convergent migration, or move against an obstacle.

By means of electron microscopy it is shown that two closely spaced crystalline ZnSe nanorods connected by twinning structures can form through a self-limiting self-assembly process. These colloidal nanorod couples have low photoluminescence polarization anisotropy, their composition can be changed by means of a cation-exchange approach, and could be used to investigate the electronic coupling between the individual nanorods.

The unusual metallic states arising at the surface of topological insulators have generated significant interest. Now, such topologically protected states are observed by means of tunnelling spectroscopy at the solid-state interface between a topological insulator and a conventional semiconductor.

Although producing 2,5-dimethylfuran (DMF) from 5-hydroxymethylfurfural (HMF) is an attractive way to synthesize renewable fuels, achieving high yields for this reaction has proved difficult. PtCo bimetallic nanoparticle catalysts embedded in hollow carbon nanospheres now show improved catalytic performance for the hydrogenolysis of HMF to DMF (98% yield after 2 hours).

Confining light in subwavelength nanowires has posed a challenge to harnessing their potential for integrated photonic devices. Now, it is shown that a high-Q cavity can be achieved by placing a single nanowire into a groove in a photonic crystal resonator.