15,905 research outputs found
Collinear versus non-collinear magnetic order in Pd atomic clusters: ab-initio calculations
We present a thorough theoretical assessment of the stability of
non-collinear spin arrangements in small palladium clusters. We generally find
that ferromagnetic order is always preferred, but that antiferromagnetic and
non-collinear configurations of different sorts exist and compete for the first
excited isomers. We also show that the ground state is insensitive to the
choice of atomic configuration for the pseudopotential used and to the
approximation taken for the exchange and correlation potential. Moreover, the
existence and relative stability of the different excited configurations also
depends weakly on the approximations employed. These results provide strong
evidence on the transferability of pseudopotential and exchange and correlation
functionals for palladium clusters as opposed to the situation found for the
bulk phases of palladium.Comment: 5 pages, 4 figure
Effects of Bose-Einstein Condensation on forces among bodies sitting in a boson heat bath
We explore the consequences of Bose-Einstein condensation on
two-scalar-exchange mediated forces among bodies that sit in a boson gas. We
find that below the condensation temperature the range of the forces becomes
infinite while it is finite at temperatures above condensation.Comment: 10 pages, 2 figure
Spontaneous CPT Violation in Confined QED
Symmetry breaking induced by untwisted fermions in QED in a nonsimply
connected spacetime with topology is investigated. It is
found that the discrete CPT symmetry of the theory is spontaneously broken by
the appearance of a constant vacuum expectation value of the electromagnetic
potential along the direction of space periodicity. The constant potential is
shown to be gauge nonequivalent to zero in the nonsimply connected spacetime
under consideration. Due to the symmetry breaking, one of the electromagnetic
modes of propagation is massive with a mass that depends on the inverse of the
compactification length. As a result, the system exhibits a sort of topological
directional superconductivity.Comment: 6 pages, revte
Structure and electronic properties of molybdenum monoatomic wires encapsulated in carbon nanotubes
Monoatomic chains of molybdenum encapsulated in single walled carbon
nanotubes of different chiralities are investigated using density functional
theory. We determine the optimal size of the carbon nanotube for encapsulating
a single atomic wire, as well as the most stable atomic arrangement adopted by
the wire. We also study the transport properties in the ballistic regime by
computing the transmission coefficients and tracing them back to electronic
conduction channels of the wire and the host. We predict that carbon nanotubes
of appropriate radii encapsulating a Mo wire have metallic behavior, even if
both the nanotube and the wire are insulators. Therefore, encapsulating Mo
wires in CNT is a way to create conductive quasi one-dimensional hybrid
nanostructures.Comment: 8 pages, 10 figure
Impact of dimerization and stretching on the transport properties of molybdenum atomic wires
We study the electrical and transport properties of monoatomic Mo wires with
different structural characteristics. We consider first periodic wires with
inter-atomic distances ranging between the dimerized wire to that formed by
equidistant atoms. We find that the dimerized case has a gap in the electronic
structure which makes it insulating, as opposed to the equidistant or
near-equidistant cases which are metallic. We also simulate two conducting
one-dimensional Mo electrodes separated by a scattering region which contains a
number of dimers between 1 and 6. The characteristics strongly depend on
the number of dimers and vary from ohmic to tunneling, with the presence of
different gaps. We also find that stretched chains are ferromagnetic.Comment: 8 pages, 7 figure
Color Magnetic Flux Tubes in Dense QCD
QCD is expected to be in the color-flavor locking phase in high baryon
density, which exhibits color superconductivity. The most fundamental
topological objects in the color superconductor are non-Abelian vortices which
are topologically stable color magnetic flux tubes. We present numerical
solutions of the color magnetic flux tube for diverse choices of the coupling
constants. We also analytically study its asymptotic profiles and find that
they are different from the case of usual superconductors. We propose the width
of color magnetic fluxes and find that it is larger than naive expectation of
the Compton wave length of the massive gluon when the gluon mass is larger than
the scalar mass.Comment: 24 pages, 5 figures; v2: typos corrected, references added, minor
changes; v3: published versio
Exact Kohn-Sham eigenstates versus quasiparticles in simple models of strongly correlated electrons
We present analytic expressions for the exact density functional and
Kohn-Sham Hamiltonian of simple tight-binding models of correlated electrons.
These are the single- and double-site versions of the Anderson, Hubbard and
spinless fermion models. The exact exchange and correlation potentials are
fully non-local. The analytic expressions allow to compare the Kohn-Sham
eigenstates of exact density functional theory with the many-body
quasi-particle states of these correlated-electron systems. The exact Kohn-Sham
spectrum describes correctly many of the non-trivial features of the many-body
quasi-particle spectrum, as for example the precursors of the Kondo peak.
However, we find that some pieces of the quasi-particle spectrum are missing
because the many-body phase-space for electron and hole excitations is richer
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