Optical trapping is a powerful manipulation and measurement technique widely used in the biological and materials sciences. Miniaturizing optical trap instruments onto optofluidic platforms holds promise for high-throughput lab-on-a-chip applications. However, a persistent challenge with existing optofluidic devices has been achieving controlled and precise manipulation of trapped particles. Here, we report a new class of on-chip optical trapping devices.

We review recent experiments in which superfluid 3He has been studied under highly controlled confinement in nanofluidic sample chambers. We discuss the experimental challenges and their resolution. These methods open the way to a systematic investigation of the superfluidity of 3He films, and the surface and edge excitations of topological superfluids. © 2014 Springer Science+Business Media New York.

Identifying the effects of surface-bulk coupling is a key challenge in exploiting the topological nature of the surface states in many available three-dimensional topological “metals.†Here we combine an effective-model calculation and an ab initio slab calculation to study the effects of the lowest order surface-bulk interaction: hybridization. In the effective-model study, we discretize an established low-energy effective four-band model and introduce hybridization between surface bands and bulk bands in the spirit of the Fano model.

We report on the fabrication and characterization of magnetic tunnel junctions consisting of a single layer of graphene as the tunnel barrier, sandwiched between two metallic ferromagnetic electrodes. We employ a fabrication process chosen to minimize oxidation of the electrode materials at the ferromagnet/graphene interfaces. The devices have low resistance-area products of 1.5-6 m2, with low-temperature magnetoresistances of 1.5-3.4%. The temperature and bias dependencies of the resistance confirm that transport is dominated by tunneling processes rather than by any unintended pinholes.

The optical properties of graphene are strongly affected by electron-electron (e-e) and electron-hole (e-h) interactions. Here we tune these many-body interactions through varying the density of free charge carriers. Measurements from the infrared to the ultraviolet reveal significant changes in the optical conductivity of graphene for both electron and hole doping. The shift, broadening, and modification in shape of the saddle-point exciton resonance reflect strong screening of the many-body interactions by the carriers, as well as changes in quasiparticle lifetimes.

Comparing the entropies of hard spheres in the limit of close packing, for different stacking sequences of the hexagonal layers, has been a challenge because the differences are so small. Here we present a method based on a "sticky-sphere" model by which the system interpolates between hard spheres in one limit and a harmonic crystal in the other. For the fcc and hcp stackings we have calculated the entropy difference in the harmonic (sticky) limit, as well as the differences in the free energy change upon removing the stickiness in the model.

We have characterized the effect of molecular weight distribution on slip of linear 1,4-polybutadiene samples sandwiched between cover glass and silicon wafer. Monodisperse polybutadiene samples with molecular weights in the range of 4-195 kg/mol and their binary mixtures were examined at steady state in planar Couette flow using tracer particle velocimetry. Slip velocity was measured at shear rates over the range of ∼0.1-15 s-1. Our results revealed that weakly entangled short chains play a crucial role in wall slip and flow dynamics of linear polymer melts.

The existence of electronic symmetry breaking in the underdoped cuprates and its disappearance with increased hole density p are now widely reported. However, the relation between this transition and the momentum-space (k →-space) electronic structure underpinning the superconductivity has not yet been established. Here, we visualize the Q→ = 0 (intra-unit-cell) and Q→ ≠ 0 (density-wave) broken-symmetry states, simultaneously with the coherent k→-space topology, for Bi2Sr2CaCu2O8+δ samples spanning the phase diagram 0.06 ≤ p ≤ 0.23.

To date, high-resolution (<1. nm) imaging of extended objects in three-dimensions (3D) has not been possible. A restriction known as the Crowther criterion forces a tradeoff between object size and resolution for 3D reconstructions by tomography. Further, the sub-Angstrom resolution of aberration-corrected electron microscopes is accompanied by a greatly diminished depth of field, causing regions of larger specimens (>6. nm) to appear blurred or missing.

A novel strategy for fabrication of ordered ceramic-metal nanocomposites was demonstrated by multifunctional block copolymer/metal nanoparticle self-assembly. Hybrid organic-inorganic block copolymer poly(3- methacryloxypropyl-T8-heptaisobutyl-polyhedral oligomeric silsesquioxane-block- N,N-dimethylaminoethyl methacrylate) was synthesized and used as a bi-functional structure directing agent for ligand-stabilized platinum nanoparticles to form ordered organic-inorganic nanocomposites with dense loading of inorganic species in both microphase separated domains.