ALBERT

Description: Decomposition of oxalic acid in the presence of water was examined in a hydrothermal diamond-anvil cell up to 800 °C and 970–1480 MPa as a function of oxygen fugacity to assess its usefulness as a C-O-H fluid source in petrologic experiments. Fluid, vapor, and solid species were identified in situ at elevated temperature and pressure with Raman spectroscopy and optical microscopy. Under oxidizing conditions (buffered by the reaction NiO Ni+1/2O 2 ), oxalic acid decomposes to carbon dioxide and water. Under reducing conditions (buffered by the reaction Mo+O 2 MoO 2 ), oxalic acid decomposes to methane and hydrogen. Under unbuffered conditions, at intermediate oxygen fugacity (~0 to 1 log units below the fayalite-quartz-magnetite buffer), oxalic acid disproportionates to graphite and minor methane and carbon dioxide. The results from the Ni-NiO-buffered and Mo-MoO 2 -buffered experiments result in observed fluid species that are similar to those predicted by previous investigations. However, there are substantial differences between our results and previous studies of oxalic acid decomposition in the unbuffered experiment that was within a log unit of the fayalite-magnetite-quartz (FMQ) buffer. These include the detection of aqueous C-H species at temperatures as low as 400 °C and a solid graphite-like phase at 800 °C. These differences can be explained if we consider that aqueous H 2 in our experiment reacted to form the C-H species, instead of being lost via diffusion through the H 2 -permeable capsules used in previous studies. Consequently, for experiments within about 1 log unit of the FMQ buffer curve, oxalic acid is likely a poor choice for a C-O-H fluid source because the formation of graphitic carbon would result in significant deviations from the expected C-O-H fluid composition and concentration (i.e., CO 2 +H 2 O). At oxygen fugacities outside a log unit of FMQ, the observed fluid species are similar to those predicted by previous investigations and the use of oxalic acid as a C-O-H fluid source is permissible from the perspective of oxygen fugacity, although other system parameters (e.g., sample geometries, capsule thickness, capsule materials, gasket materials, wall thickness) must still be considered.

Description: We demonstrate a tunnel diode composed of a vertical MoS 2 /SiO 2 /Si heterostructure. A MoS 2 flake consisting four areas of different thicknesses functions as a gate terminal of a silicon field-effect transistor. A thin gate oxide allows tunneling current to flow between the n-type MoS 2 layers and p-type Si channel. The tunneling-current characteristics show multiple negative differential resistance features, which we interpret as an indication of different conduction-band alignments of the MoS 2 layers of different thicknesses. The presented tunnel device can be also used as a hybrid-heterostructure device combining the advantages of two-dimensional materials with those of silicon transistors.

Description: Due to their interesting orientation-dependent properties, the ability to grow high-index semiconductor crystals and nanostructures extends the design palette for applications based on these materials. Notably, a source containing a systematic reporting of what the Raman tensors are for an arbitrary high-index zincblende material is yet to appear in the literature. Herein, we present the polarized Raman backscattering selection rules for arbitrary ( hhl )-oriented diamond- and zincblende-type crystal surfaces and verify their correctness through experiment (up to (115)). Considering the many degrees of freedom available to common polarized micro-Raman scattering instruments, and the unique local orientation of the probed material, we further examine a range of consequences imposed by the selection rules for the Raman backscattering method.

Description: Corrigendum Nature Communications doi: 10.1038/ncomms6463 Authors: G. Buchs, S. Bagiante, G. A. Steele

Description: We study the mechanical dissipation of the fundamental mode of millimeter-sized, high quality-factor ( Q ) metalized silicon nitride membranes at temperatures down to 14 mK using a three-dimensional optomechanical cavity. Below 200 mK, high- Q modes of the membranes show a diverging increase of Q with decreasing temperature, reaching Q = 1.27 × 10 8 at 14 mK, an order of magnitude higher than that reported before. The ultra-low dissipation makes the membranes highly attractive for the study of optomechanics in the quantum regime, as well as for other applications of optomechanics such as microwave to optical photon conversion.

Description: Abstract The predator satiation hypothesis posits that masting helps plants escape seed predation through starvation of predators in lean years, followed by satiation of predators in mast years. Importantly, successful satiation requires sufficiently delayed bottom‐up effects of seed availability on seed consumers. However, some seed consumers may be capable of quick aggregative and reproductive responses to masting, which may jeopardize positive density dependence of seed survival. We used a 17‐yr data set on seed production and insect (Curculio weevils) infestation of three North American oaks species (northern red Quercus rubra, white Q. alba, and chestnut oak Q. montana) to test predictions of the predation satiation hypothesis. Furthermore, we tested for the unlagged numerical response of Curculio to acorn production. We found that masting results in a bottom‐up effect on the insect population; both through increased reproductive output and aggregation at seed‐rich trees. Consequently, mast seeding in two out of three studied oaks (white and chestnut oak) did not help to escape insect seed predation, whereas, in the red oak, the escape depended on the synchronization of mast crops within the population. Bottom‐up effects of masting on seed consumer populations are assumed to be delayed, and therefore to have negligible effects on seed survival in mast years. Our research suggests that insect populations may be able to mount rapid reproductive and aggregative responses when seed availability increases, possibly hindering satiation effects of masting. Many insect species are able to quickly benefit from pulsed resources, making mechanisms described here potentially relevant in many other systems.

Description: Author(s): Edward A. Laird, Ferdinand Kuemmeth, Gary A. Steele, Kasper Grove-Rasmussen, Jesper Nygård, Karsten Flensberg, and Leo P. Kouwenhoven Carbon nanotubes with multifunctional capabilities are prime candidates for quantum wires for use in a variety of novel electronic devices. Unlike conventional semiconductor nanowires, electrons confined to nanotubes have two angular momentum quantum numbers from spin and valley degrees of freedom. This review describes the energy levels associated with the interplay of each of these degrees of freedom and how the spin-orbit interaction affects electronic transport through single and multiple quantum dots created by external field gating. The emphasis on experimental evidence provides essential concepts which are placed into context with recent theoretical advances such as on electron-electron interactions in one dimension. [Rev. Mod. Phys. 87, 703] Published Tue Jul 28, 2015

Description: Article Optomechanics is the use of light to control the motion of a mechanical resonator, potentially cooling it to the quantum ground state. Here, the authors cool a millimetre-scale silicon nitride membrane to an effective temperature of 34 microkelvin by coupling it to a three-dimensional microwave cavity. Nature Communications doi: 10.1038/ncomms9491 Authors: Mingyun Yuan, Vibhor Singh, Yaroslav M. Blanter, Gary A. Steele

Description: A new phase of ammonium nitrate (AN) is found using first principles evolutionary crystal structure search. It is this polymorph that is associated with the phase transition to previously unidentified phase, which was detected in experiment at 17 GPa upon appearance of the two extra peaks in Raman spectrum. The new phase has a monoclinic unit cell in the P2 1 /m space group symmetry (AN-P2 1 /m) and is similar to the known phase IV of AN (AN-IV) except the ammonium molecules are oriented differently relative to the nitrate molecules. The calculated free energy of AN-P2 1 /m is found to be lower than AN-IV at pressures above 10.83 GPa. The equation of state of both AN-P2 1 /m and AN-IV phases (volume vs hydrostatic pressure at room temperature) has been obtained within the quasi-harmonic approximation. The calculated Raman spectrum of both AN-P2 1 /m and AN-IV as a function of pressure is in a good agreement with experiment. The energetic competitiveness of AN-IV and AN-P2 1 /m at ambient conditions suggests a possibility of the phase transition in a small pressure-temperature range near ambient pressure and temperature.

Description: Author(s): Vibhor Singh, Olga Shevchuk, Ya. M. Blanter, and Gary A. Steele We experimentally investigate the nonlinear response of a multilayer graphene resonator using a superconducting microwave cavity to detect its motion. The radiation pressure force is used to drive the mechanical resonator in an optomechanically induced transparency configuration. By varying the ampl… [Phys. Rev. B 93, 245407] Published Thu Jun 09, 2016