Briefly emerging from my end-of-semester fog, here are some interesting preprints from the past week.
The graphene craze continues unabated. Remember how the superconductivity community descended upon MgB2 and made every superconductivity-related measurement under the sun on the new material in a feeding frenzy? A similar phenomena is taking place with the 2d electron community and graphene. Fortunately, graphene seems to be pretty neat stuff! For example:
arxiv:0704.3165 - Hill et al., Graphene spin valve devices
People have done normal metal contacts to graphene, and superconducting contacts to graphene, so what's left but ferromagnetic contacts to graphene? Unsurprisingly you can use ferromagnetic electrodes to inject spin into graphene, and its such a low-Z material of high purity that both spin-orbit scattering and spin flip scattering from impurities are minimal, leading to real spintronic possibilities in this stuff.
Further exploiting the robustness of graphene even under significant processing:
arxiv:0704.2626 - Huard et al., Transport measurements across a tunable potential barrier in graphene
arxiv:0704.3487 - Williams et al., Quantum Hall Effect in a graphene pn junction
arxiv:0704.3608 - Abanin and Levitov, Quantized transport in graphene pn junctions in magnetic field
Because graphene is a high quality 2d material and can be shifted readily from n and p carriers via doping or gating, it is possible to set up sophisticated structures (npn or pnp junctions; pn junctions) while preserving long mean free paths. The result is rich phenomenology, as seen in the first two (experimental) papers listed here, and analyzed in detail in the third (theory) paper. I'm still waiting for a really unexpected graphene result that isn't readily explained.
Two other papers that involve tunable model systems to examine strong correlation physics:
arxiv:0704.3011 - Bloch et al., Many-body physics with ultracold gases
This is a review article about using cold atoms to look at nontrivial correlation effects. One holy grail in this business is to use strongly interacting cold fermions in a 2d optical lattice to explicitly simulate the Hubbard model (relevant to high-Tc superconductivity), a topic of much interest to one of my faculty colleagues.
arxiv:0704.2614 - Walsh et al., Screening of excitons in single, suspended carbon nanotubes
Carbon nanotubes have 1d band structures, and therefore are subject to strong electron-electron interaction effects and poor screening. The consequence of these interactions is the demise of Fermi liquid theory, and therefore the onset of the fractionalized quasiparticles (spinons and holons) of Luttinger liquid theory. Excitons are also strongly modified in these systems. One way to probe these effects is to change the effective interaction; this is done by using immersion in dielectric media to change the screening of charges, and the effects are probed spectroscopically.