4,355 research outputs found
Boron Spectral Density and Disorder Broadening in B-doped Diamond
Comparison of periodic B dopants with a random alloy of substitional boron in
diamond is carried out using several supercells and the coherent potential
approximation (CPA) for the random alloy case. The main peak in the B local
density of states is shifted to lower binding energy compared to the
corresponding C peak in intrinsic diamond. In supercells, this shows up as
strongly B-character bands split from bulk C bands away from the zone center,in
an energy region around -1 eV. Even for a 4*4*4 supercell (BC), effects
of the dopant order are evident in the form of primarily B-character bands just
below the Fermi level at the supercell zone boundary. The bands resulting from
the CPA are of continuous mixed C-B character. They resemble virtual crystal
bands, but broadened somewhat reflecting the disorder-induced lifetime, and are
consistent with angle-resolved photoemission band maps. The B character is 1.7
times larger than for C (per atom) near the top of the valence bands for CPA,
and roughly the same for supercells. CPA results are particularly useful since
they characterize the wavevector and energy dependence of disorder broadening.Comment: 8 pages and 9 embedded figures (To appear in PRB
Ground states with cluster structures in a frustrated Heisenberg chain
We examine the ground state of a Heisenberg model with arbitrary spin S on a
one-dimensional lattice composed of diamond-shaped units. A unit includes two
types of antiferromagnetic exchange interactions which frustrate each other.
The system undergoes phase changes when the ratio between the
exchange parameters varies. In some phases, strong frustration leads to larger
local structures or clusters of spins than a dimer. We prove for arbitrary S
that there exists a phase with four-spin cluster states, which was previously
found numerically for a special value of in the S=1/2 case. For S=1/2
we show that there are three ground state phases and determine their
boundaries.Comment: 4 pages, uses revtex.sty, 2 figures available on request from
[email protected], to be published in J. Phys.: Cond. Mat
Documentation of the GLAS fourth order general circulation model. Volume 1: Model documentation
The volume 1, of a 3 volume technical memoranda which contains a documentation of the GLAS Fourth Order General Circulation Model is presented. Volume 1 contains the documentation, description of the stratospheric/tropospheric extension, user's guide, climatological boundary data, and some climate simulation studies
Documentation of the GLAS fourth order general circulation model. Volume 2: Scalar code
Volume 2, of a 3 volume technical memoranda contains a detailed documentation of the GLAS fourth order general circulation model. Volume 2 contains the CYBER 205 scalar and vector codes of the model, list of variables, and cross references. A variable name dictionary for the scalar code, and code listings are outlined
Documentation of the GLAS fourth order general calculation model. Volume 3: Vectorized code for the Cyber 205
Volume 3 of a 3-volume technical memoranda which contains documentation of the GLAS fourth order genera circulation model is presented. The volume contains the CYBER 205 scalar and vector codes of the model, list of variables, and cross references. A dictionary of FORTRAN variables used in the Scalar Version, and listings of the FORTRAN Code compiled with the C-option, are included. Cross reference maps of local variables are included for each subroutine
Comment on "c-axis Josephson tunneling in -wave superconductors''
This comment points out that the recent paper by Maki and Haas [Phys. Rev. B
{\bf 67}, 020510 (2003)] is completely wrong.Comment: 1 page, submittted to Phys. Rev.
Multi-Component Dark Matter Systems and Their Observation Prospects
Conversions and semi-annihilations of dark matter (DM) particles in addition
to the standard DM annihilations are considered in a three-component DM system.
We find that the relic abundance of DM can be very sensitive to these
non-standard DM annihilation processes, which has been recently found for
two-component DM systems. To consider a concrete model of a three-component DM
system, we extend the radiative seesaw model of Ma by adding a Majorana fermion
\chi and a real scalar boson \phi, to obtain a Z_2 \times Z'_2 DM stabilizing
symmetry, where we assume that the DM particles are the inert Higgs boson, \chi
and \phi. It is shown how the allowed parameter space, obtained previously in
the absence of \chi and \phi, changes. The semi-annihilation process in this
model produces monochromatic neutrinos. The observation rate of these
monochromatic neutrinos from the Sun at IceCube is estimated. Observations of
high energy monochromatic neutrinos from the Sun may indicate a multi-component
DM system.Comment: 27 pages, 11 figure
Room-temperature ferromagnetism in Sr_(1-x)Y_xCoO_(3-delta) (0.2 < x < 0.25)
We have measured magnetic susceptibility and resistivity of
SrYCoO ( 0.1, 0.15, 0.2, 0.215, 0.225, 0.25, 0.3,
and 0.4), and have found that SrYCoO is a room
temperature ferromagnet with a Curie temperature of 335 K in a narrow
compositional range of 0.2 0.25. This is the highest transition
temperature among perovskite Co oxides. The saturation magnetization for
0.225 is 0.25 /Co at 10 K, which implies that the observed
ferromagnetism is a bulk effect. We attribute this ferromagnetism to a peculiar
Sr/Y ordering.Comment: 5 pages, 4 figure
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