3,019 research outputs found
Chiral single-wall gold nanotubes
Based on first-principles calculations we show that gold atoms can form both
free-standing and tip-suspended chiral single-wall nanotubes composed of
helical atomic strands. Free-standing, infinite (5,5) tube is found to be
energetically the most favorable. While energetically less favorable, the
experimentally observed (5,3) tube stretching between two tips corresponds to a
local minimum in the string tension. Similarly, the (4,3) tube is predicted as
a favorable structure yet to be observed experimentally. Analysis of band
structure, charge density, and quantum ballistic conductance suggests that the
current on these wires is less chiral than expected, and there is no direct
correlation between the numbers of conduction channels and helical strands.Comment: Figures provided in eps forma
Strange Particles and Neutron Stars - Experiments at Gsi
Experiments on strangeness production in nucleus-nucleus collisions at SIS
energies address fundamental aspects of modern nuclear physics: the
determination of the nuclear equation-of-state at high baryon densities and the
properties of hadrons in dense nuclear matter. Experimental data and
theoretical results will be reviewed. Future experiments at the FAIR
accelerator aim at the exploration of the QCD phase diagram at highest baryon
densities.Comment: %Invited talk given at the International Invited talk given at the
International Symposium on Heavy Ion Physics (ISHIP 2006) April 3-6 2006,
FIAS, Frankfurt, Germany Frankfurt, German
Ab-initio electron transport calculations of carbon based string structures
First-principles calculations show that monatomic strings of carbon have high
cohesive energy and axial strength, and exhibit stability even at high
temperatures. Due to their flexibility and reactivity, carbon chains are
suitable for structural and chemical functionalizations; they form also stable
ring, helix, grid and network structures. Analysis of electronic conductance of
various infinite, finite and doped string structures reveal fundamental and
technologically interesting features. Changes in doping and geometry give rise
to dramatic variations in conductance. In even-numbered linear chains strain
induces substantial decrease of conductance. The double covalent bonding of
carbon atoms underlies their unusual chemical, mechanical and transport
properties.Comment: 4 pages, 4 figure
Monolayer honeycomb structures of group IV elements and III-V binary compounds
Using first-principles plane wave calculations, we investigate two
dimensional honeycomb structure of Group IV elements and their binary
compounds, as well as the compounds of Group III-V elements. Based on structure
optimization and phonon mode calculations, we determine that 22 different
honeycomb materials are stable and correspond to local minima on the
Born-Oppenheimer surface. We also find that all the binary compounds containing
one of the first row elements, B, C or N have planar stable structures. On the
other hand, in the honeycomb structures of Si, Ge and other binary compounds
the alternating atoms of hexagons are buckled, since the stability is
maintained by puckering. For those honeycomb materials which were found stable,
we calculated optimized structures, cohesive energies, phonon modes, electronic
band structures, effective cation and anion charges, and some elastic
constants. The band gaps calculated within Density Functional Theory using
Local Density Approximation are corrected by GW0 method. Si and Ge in honeycomb
structure are semimetal and have linear band crossing at the Fermi level which
attributes massless Fermion character to charge carriers as in graphene.
However, all binary compounds are found to be semiconductor with band gaps
depending on the constituent atoms. We present a method to reveal elastic
constants of 2D honeycomb structures from the strain energy and calculate the
Poisson's ratio as well as in-plane stiffness values. Preliminary results show
that the nearly lattice matched heterostructures of ...Comment: 12 Pages, 7 Figures, 1 Table;
http://link.aps.org/doi/10.1103/PhysRevB.80.15545
Half-metallic properties of atomic chains of carbon-transition metal compounds
We found that magnetic ground state of one-dimensional atomic chains of
carbon-transition metal compounds exhibit half-metallic properties. They are
semiconductors for one spin-direction, but show metallic properties for the
opposite direction. The spins are fully polarized at the Fermi level and net
magnetic moment per unit cell is an integer multiple of Bohr magneton. The
spin-dependent electronic structure can be engineered by changing the number of
carbon and type of transition metal atoms. These chains, which are stable even
at high temperature and some of which keep their spin-dependent electronic
properties even under moderate axial strain, hold the promise of potential
applications in nanospintronics.Comment: 11 pages, 3 figures, 1 table
Testing Lorentz Invariance by Comparing Light Propagation in Vacuum and Matter
We present a Michelson-Morley type experiment for testing the isotropy of the
speed of light in vacuum and matter. The experiment compares the resonance
frequency of a monolithic optical sapphire resonator with the resonance
frequency of an orthogonal evacuated optical cavity made of fused silica while
the whole setup is rotated on an air bearing turntable once every 45 s.
Preliminary results yield an upper limit for the anisotropy of the speed of
light in matter (sapphire) of \Delta c/c < 4x10^(-15), limited by the frequency
stability of the sapphire resonator operated at room temperature. Work to
increase the measurement sensitivity by more than one order of magnitude by
cooling down the sapphire resonator to liquid helium temperatures (LHe) is
currently under way.Comment: Presented at the Fifth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 28-July 2, 201
Spintronic properties of zigzag-edged triangular graphene flakes
Cataloged from PDF version of article.We investigate quantum transport properties of triangular graphene flakes with zigzag edges by using first principles calculations. Triangular graphene flakes have large magnetic moments which vary with the number of hydrogen atoms terminating its edge atoms and scale with its size. Electronic transmission and current-voltage characteristics of these flakes, when contacted with metallic electrodes, reveal spin valve and remarkable rectification features. The transition from ferromagnetic to antiferromagnetic state under bias voltage can, however, terminate the spin polarizing effects for specific flakes. Geometry and size dependent transport properties of graphene flakes may be crucial for spintronic nanodevice applications. (C) 2010 American Institute of Physics. [doi:10.1063/1.3489919
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