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Abstract:

Topological insulators exhibit a metallic surface state in which the directions of the carriers' momentum and spin are locked together. This characteristic property, which lies at the heart of proposed applications of topological insulators, protects carriers in the surface state from back-scattering unless the scattering centres are time-reversal symmetry breaking (i.e. magnetic). Here, we introduce a method of probing the effect of magnetic scattering by decorating the surface of topological insulators with molecules, whose magnetic degrees of freedom can be engineered independently of their electrostatic structure. We show that this approach allows us to separate the effects of magnetic and non-magnetic scattering in the perturbative limit. We thereby confirm that the low-temperature conductivity of SmB6 is dominated by a surface state and that the momentum of quasiparticles in this state is particularly sensitive to magnetic scatterers, as expected in a topological insulator.

Abstract:

Future lipid membrane-associated DNA nanostructures are expected to find applications ranging from synthetic biology to nanomedicine. Here we have designed and synthesized DNA tiles and modified them by amphiphilic covalent moieties. dod-DEG groups, which consist of a hydrophilic diethylene glycol (DEG) and a hydrophobic dodecyl group, are introduced at the phosphate backbone to create amphiphilic DNA strands which are subsequently introduced into one face of DNA tiles. In this way the tile becomes able to stably bind to lipid membranes by insertion of the hydrophobic groups inside the bilayer core. The functionalized tiles do not aggregate in solution. Our results show that these amphiphilic DNA tiles can bind and assemble into 2D lattices on both gel and fluid lipid bilayers. The binding of the DNA structures to membranes is dependent on the lipid phase of the membrane, the concentration of Mg2+ cation, the length of the amphiphilic modifications to the DNA as well as on the density of the modifications within the tile. Atomic force microscopy–based force spectroscopy is used to investigate the effect of the inserted DNA tiles on the mechanical properties of the lipid membranes. The results indicate that the insertion of DNA tiles produces an approx. 20% increase of the bilayer breakthrough force.

Abstract:

We demonstrate, for the first time, confinement of the orientation of graphitic micro-flakes to a well-defined plane in solution by applying two perpendicular fields: a vertical static magnetic field and a horizontal time-varying electric field.