96 research outputs found
Erklärung der Sektionen Sportgeschichte und Sportphilosophie in der Deutschen Vereinigung für Sportwissenschaft zur Förderung der geistes- und kulturwissenschaftlichen Teildisziplinen
No full textErklärung der Sektionen Sportgeschichte und Sportphilosophie in der Deutschen Vereinigung für Sportwissenschaft zur Förderung der geistes- und kulturwissenschaftlichen Teildisziplinen
No full textGate-Tunable Magnetism and Giant Magnetoresistance in Suspended Rhombohedral-Stacked Few-Layer Graphene
No full textConventionally, magnetism arises from the strong exchange interaction among the magnetic moments of d- or f-shell electrons. It can also emerge in perfect lattices from nonmagnetic elements, such as that exemplified by the Stoner criterion. Here we report tunable magnetism in suspended rhombohedral-stacked few-layer graphene (r-FLG) devices with flat bands. At small doping levels (n ∼ 1011 cm–2), we observe prominent conductance hysteresis and giant magnetoconductance that exceeds 1000% as a function of magnetic fields. Both phenomena are tunable by density and temperature and disappear at n > 1012 cm–2 or T > 5 K. These results are confirmed by first-principles calculations, which indicate the formation of a half-metallic state in doped r-FLG, in which the magnetization is tunable by electric field. Our combined experimental and theoretical work demonstrate that magnetism and spin polarization, arising from the strong electronic interactions in flat bands, emerge in a system composed entirely of carbon atoms
Room-temperature resonant tunneling of electrons in carbon nanotube junction quantum wells
No full textResonant tunneling structures [M. Bockrath, W. Liang, D. Bozovic, J. H. Hafner, C. B. Lieber, M. Tinkham, and H. Park, Science 291, 283 (2001)], formed between the junction of two single walled nanotubes and the conductive atomic force microscopy tip contact were investigated using current sensing atomic force microscopy. Oscillations in the current voltage characteristics were measured at several positions of the investigated nanotube. The oscillatory behavior is shown to follow a simple quantum mechanical model, dependent on the energy separation in the quantum well formed within the two junctions. Our model shows that these observations seen over several hundreds of nanometers, are possible only if the scattering cross section at defects is small resulting in long phase coherence length, and if the effective mass of the carrier electrons is small. We have calculated the approximate mass of the conduction electrons to be 0.003 me. © 2005 American Institute of Physics
Revival of Electron Coherence in a Quantum Wire of Finite Length
No full textWe study the spatial decay of electron coherence due to electron-electron interaction in a finite-length disorder-free quantum wire. Based on the Luttinger liquid theory, we demonstrate that the coherence length characterizing the exponential decay of the coherence can vary from region to region, and that the coherence can even revive after the decay. This counterintuitive behavior, which is in clear contrast to the conventional exponential decay with single coherence length, is due to the fractionalization of an electron and the finite-size-induced recombination of the fractions.We thank M. Bockrath and A. Braggio for discussion.
This work was supported by KRF (2006-331-C00118)
Hydrogen Storage Properties of Metal Nitroprussides M[Fe(CN)<sub>5</sub>NO], (M = Co, Ni)
No full textThe volumetric hydrogen adsorption isotherms of two isostructural dehydrated cubic metal nitroprussides
M[Fe(CN)5NO] (M = Co2+, Ni2+) have been measured up to a pressure of 760 Torr at 77 and 87 K. These
materials are among the most efficient H2 sorbents based on porous coordination polymers reported to date.
The H2 uptake in both materials is ∼1.6 wt % at 77 K and 760 torr. These H2 capacities match those reported
recently in the structurally related M3[Co(CN)6]2 compounds and are approximately 25% higher than those
reported for Zn4O(1,4-benzenedicarboxylate)3 under the same conditions of temperature and pressure. The
isosteric heats of H2 adsorption calculated from the 77 and 87 K isotherms for both materials were found to
vary from ∼7.5 kJ/mol at 0.40 wt % coverage to ∼5.5 kJ/mol at 1.2 wt % coverage. The N2 BET surface
areas were determined to be 634 m2/g and 523 m2/g for M = Ni and M = Co, respectively
Protonation Rate Constants and Optical Absorption Spectra of Benzyl Carbanion Pairs in Tetrahydrofuran Solution
No full textIonic Aggregation of the Solvated Electron With Lithium Cation in Tetrahydrofuran Solution
No full textStacking-dependent band gap and quantum transport in trilayer graphene
No full textGraphene is an extraordinary two-dimensional (2D) system with chiral charge carriers and fascinating electronic, mechanical and thermal properties. In multilayer graphene, stacking order provides an important yet rarely explored degree of freedom for tuning its electronic properties. For instance, Bernal-stacked trilayer graphene (B-TLG) is semi-metallic with a tunable band overlap, and rhombohedral-stacked trilayer graphene (r-TLG) is predicted to be semiconducting with a tunable band gap. These multilayer graphenes are also expected to exhibit rich novel phenomena at low charge densities owing to enhanced electronic interactions and competing symmetries. Here we demonstrate the dramatically different transport properties in TLG with different stacking orders, and the unexpected spontaneous gap opening in charge neutral r-TLG. At the Dirac point, B-TLG remains metallic, whereas r-TLG becomes insulating with an intrinsic interaction-driven gap ~6 meV. In magnetic fields, well-developed quantum Hall (QH) plateaux in r-TLG split into three branches at higher fields. Such splitting is a signature of the Lifshitz transition, a topological change in the Fermi surface, that is found only in r-TLG. Our results underscore the rich interaction-induced phenomena in trilayer graphene with different stacking orders, and its potential towards electronic applications
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