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.

We investigate the effect of a direct current on propagating spin waves in a CoFeB/Ta bilayer structure. Using the micro-Brillouin light scattering technique, we observe that the spin-wave damping and amplitude may be attenuated or amplified depending on the direction of the current and the applied magnetic field. Our work suggests an effective approach for electrically controlling the propagation of spin waves in a magnetic waveguide and may be useful in a number of applications such as phase-locked nano-oscillators and hybrid information-processing devices.

Unicellular eukaryotic amoebae Dictyostelium discoideum are generally believed to grow in their vegetative state as single cells until starvation, when their collective aspect emerges and they differentiate to form a multicellular slime mold. While major efforts continue to be aimed at their starvation-induced social aspect, our understanding of population dynamics and cell cycle in the vegetative growth phase has remained incomplete. Here we show that cell populations grown on a substrate spontaneously synchronize their cell cycles within several hours.

Classical density-functional theory is the most direct approach to equilibrium structures and free energies of inhomogeneous liquids, but requires the construction of an approximate free-energy functional for each liquid of interest. We present a general recipe for constructing functionals for small-molecular liquids based only on bulk experimental properties and ab initio calculations of a single solvent molecule.