Research articles

Topological crystalline insulators are characterized by metallic states originating from crystal symmetries. A transistor device that takes advantage of the quantum properties of the topological crystalline insulating materials SnTe and Pb_1−xSn_xSe(Te) is now proposed.

The friction of surfaces in relative motion and separated by a few nanometres is thought to be dominated by electronic effects. It is now found that the friction sensed by an AFM tip oscillating above a NbSe₂ surface takes the form of giant dissipation peaks, and that the peaks are related to a hysteresis cycle where the oscillating tip locally pumps 2π slips in the phase of a charge-density wave.

Although it has been shown that engineering of conducting polymers such as poly(3,4-ethyldioxythiophene) can improve the Seebeck coefficient and the figure of merit ZT of these materials, the mechanisms underlying this improved thermoelectric behaviour are still not fully understood. It is now reported that the band structure of semicrystalline films of these bipolaronic polymers, resembling that of inorganic semi-metals used for thermoelectric applications, can explain these findings.

Understanding the thermal transport properties of superlattice structures is relevant to a number of possible practical applications. Now, the scattering of phonons in oxide superlattices is shown to undergo a crossover from an incoherent to a coherent regime, which in turn strongly alters their thermal behaviour.

Bose–Einstein condensates of exciton–polaritons have been stabilized in a range of crystalline systems. Now, polaritons are shown to condense at room temperature using a microcavity within an organic polymer.

The imaging of tumours is challenging because of the wide range of different cancers. Now, the rapid detection of tumours, independent of type, is achieved using a nonlinear amplification strategy that employs ultrasensitive pH-responsive fluorescent nanoparticles that illuminate within tumour neovasculature or in response to the tumour’s acidic extracellular environment.

The interplay between the electronic and magnetic degrees of freedom in multiferroic materials offers promise for a range of applications. Now, a technique for imaging the magnetoelectric domains directly is developed, and demonstrated on the hexagonal manganite ErMnO₃.

A requirement for the reversible mechanical actuation of liquid-crystal elastomers is macroscale alignment. However, current processing techniques do not achieve reliable and robust alignment, which limits the practical use of these materials as actuators and artificial muscles. It is now shown that by introducing polymers with exchangeable covalent bonds, liquid-crystal elastomers can be easily processed and aligned, and subsequently remodelled.

Photoelectrochemical water-splitting devices require integrating electrocatalysts with light-absorbing semiconductors, but understanding charge-transfer processes at interfaces has proved difficult. Ion-permeable electrocatalysts deposited onto TiO₂ photoelectrodes now result in adaptive semiconductor/electrocatalyst junctions where both the effective interface barrier height and the photovoltage output change depending on the oxidation state of the electrocatalyst.

In wound healing, skin cells collectively migrate to maintain tissue cohesion despite the existence of inhomogeneities in the extracellular environment within the wound bed. Yet how the cell collective responds to heterogeneities in the extracellular matrix is not well understood. Now, it is shown that migrating human keratinocyte cell sheets form suspended multicellular bridges over non-adhesive regions on micropatterned substrates comprising alternating strips of fibronectin and non-adherent polymer.

The photoluminescent properties of electron spins at nitrogen–vacancy (NV) centres are promising for use in quantum information and magnetometry. It is now shown that the coherence times of NV centres in nanodiamonds can be engineered to be comparable to those of bulk diamond.

Failure caused by dendrite growth in rechargeable batteries with lithium metal anodes has prevented their widespread applicability. A microtomography study on lithium–polymer–lithium cells now reveals that at the early stage of dendrite formation dendritic structures lie within the electrode, underneath the polymer/electrode interface.

Lanthanide-doped nanocrystals can be used to upconvert infrared radiation into visible light, and are thought to be promising for a range of photonic and biological imaging applications. It is now shown that the upconversion efficiency can be improved by appropriately clustering the lanthanide ions on different structural sublattices.

Layered oxides are promising for many applications ranging from energy conversion and storage to magnetic and electric devices. The oxygen storage ability of ferroelectric LuFe₂O_4+x is now demonstrated and the storage mechanism is believed to be governed by a complex oxygen intercalation/de-intercalation process with several intermediate metastable states.

The efficiency of organic blends used for photovoltaic applications depends on their ability to convert photoexcited charges into free holes and electrons. It is now demonstrated that the lowermost energetic states formed at the donor/acceptor interface can reach conversion efficiencies close to 100%, and therefore do not behave as traps for charge carriers.

The generation and manipulation of single photons is important for quantum information and metrology. Highly bright and stable single-photon sources are now identified in silicon carbide, a wide-bandgap semiconductor widely used for photonic and electronic devices.

The LaAlO₃/SrTiO₃ interface plays host to a diverse range of physical phenomena. By imaging the electrostatic landscape with a specially designed detector it is shown that tetragonal domains give rise to a large extrinsic piezoelectricity.

The electrochemical reduction of oxygen to hydrogen peroxide requires selective and stable electrocatalysts. It is now shown that Pt–Hg nanoparticles display an order of magnitude improvement in the mass activity for hydrogen peroxide production compared with the best performing catalyst.

The propagation of light in photonic crystals with a honeycomb structure mirrors the behaviour of charges in graphene, therefore allowing for the investigation of electronic properties that cannot otherwise be accessed in graphene itself. This approach is now used to predict unexpected edge states that localize in the bearded edges of hexagonal lattices.

Oxide ion conductors are technologically relevant for applications in electrochemical devices such as sensors, separation membranes and fuel cells. Magnesium doping in Na_0.5Bi_0.5TiO₃—a piezoelectric material that suffers from high leakage conductivity—now results in a family of ionic conductors that could prove significant not only for dielectric-based applications but also for intermediate-temperature solid-oxide fuel cells.