Topological insulators exhibit metallic surface states populated by massless Dirac fermions with spin-momentum locking, where the carrier spin lies in-plane, locked at right angles to the carrier momentum. Here, we show that a charge current produces a net spin polarization via spin-momentum locking in Bi2Se3 films, and this polarization is directly manifested as a voltage on a ferromagnetic contact. This voltage is proportional to the projection of the spin polarization onto the contact magnetization, is determined by the direction and magnitude of the charge current, scales inversely with Bi2Se3 film thickness, and its sign is that expected from spin-momentum locking rather than Rashba effects. Similar data are obtained for two different ferromagnetic contacts, demonstrating that these behaviours are independent of the details of the ferromagnetic contact. These results demonstrate direct electrical access to the topological insulators' surface-state spin system and enable utilization of its remarkable properties for future technological applications.
Magnetic skyrmions are localized non-collinear spin textures with a high potential for future spintronic applications(1-12). Skyrmion phases have been discovered in a number of materials(9,11) and a focus of current research is to prepare, detect and manipulate individual skyrmions for implementation in devices(6-8). The local experimental characterization of skyrmions has been performed by, for example, Lorentz microscopy(3) or atomic-scale tunnel magnetoresistance measurements using spin-polarized scanning tunnelling microscopy(4,7,12). Here we report a drastic change of the differential tunnel conductance for magnetic skyrmions that arises from their non-collinearity: mixing between the spin channels locally alters the electronic structure, which makes a skyrmion electronically distinct from its ferromagnetic environment. We propose this tunnelling non-collinear magnetoresistance as a reliable all-electrical detection scheme for skyrmions with an easy implementation into device architectures.
One of the fundamental hurdles in plasmonics is the trade-off between electromagnetic field confinement and the coupling efficiency with free-space light, a consequence of the large momentum mismatch between the excitation source and plasmonic modes. Acoustic plasmons in graphene, in particular, have an extreme level of field confinement, as well as an extreme momentum mismatch. Here, we show that this fundamental compromise can be overcome and demonstrate a graphene acoustic plasmon resonator with nearly perfect absorption (94%) of incident mid-infrared light. This high efficiency is achieved by utilizing a two-stage coupling scheme: free-space light coupled to conventional graphene plasmons, which then couple to ultraconfined acoustic plasmons. To realize this scheme, we transfer unpatterned large-area graphene onto template-stripped ultraflat metal ribbons. A monolithically integrated optical spacer and a reflector further boost the enhancement. We show that graphene acoustic plasmons allow ultrasensitive measurements of absorption bands and surface phonon modes in angstrom-thick protein and SiO(2 )layers, respectively. Our acoustic plasmon resonator platform is scalable and can harness the ultimate level of light-matter interactions for potential applications including spectroscopy, sensing, metasurfaces and optoelectronics.
Understanding thermal transport in nanostructured materials is important for the development of energy conversion applications(1-4) and the thermal management of microelectronic and optoelectronic devices(5). Most nanostructures interact through van der Waals interactions(6), and these interactions typically lead to a reduction in thermal transport(7-10). Here, we show that the thermal conductivity of a bundle of boron nanoribbons can be significantly higher than that of a single freestanding nanoribbon. Moreover, the thermal conductivity of the bundle can be switched between the enhanced values and that of a single nanoribbon by wetting the van der Waals interface between the nanoribbons with various solutions.
Patterning of semiconducting polymers on surfaces is important for various applications in nanoelectronics and nanophotonics. However, many of the approaches to nanolithography that are used to pattern inorganic materials are too harsh for organic semiconductors, so research has focused on optical patterning(1-3) and various soft lithographies(4). Surprisingly little attention has been paid to thermal(5), thermornecharl and thermochemical(8-13) patterning. Here, we demonstrate thermochemical nanopatterning of poly(p-phenylene vinylene), a widely used electroluminescent polymer.(14), by a scanning probe. We produce patterned structures with dimensions below 28 nm, although the tip of the probe has a diameter of 5 mu m, and achieve write speeds of 100 mu m s(-1). Experiments show that a resolution of 28 nm is possible when the tip-sample contact region has dimensions of similar to 100 nm and, on the basis of finite-element modelling we predict that the resolution could be improved by using a thinner resist layer and an optimized probe. Thermochemical lithography offers a versatile, reliable and general nanopatterning technique because a large number of optical materials, including many commercial crosslinker additives and photoresists, rely on chemical mechanisms that can also be thermally adivated(8,15,16).