21 research outputs found
Gutzwiller-Correlated Wave Functions: Application to Ferromagnetic Nickel
Ferromagnetic Nickel is the most celebrated iron group metal with pronounced
discrepancies between the experimental electronic properties and predictions of
density functional theories. In this work, we show in detail that the recently
developed multi-band Gutzwiller theory provides a very good description of the
quasi-particle band structure of nickel. We obtain the correct exchange
splittings and we reproduce the experimental Fermi-surface topology. The
correct (111)-direction of the magnetic easy axis and the right order of
magnitude of the magnetic anisotropy are found. Our theory also reproduces the
experimentally observed change of the Fermi-surface topology when the magnetic
moment is oriented along the (001)-axis. In addition to the numerical study, we
give an analytical derivation for a much larger class of variational
wave-functions than in previous investigations. In particular, we cover cases
of superconductivity in multi-band lattice systems.Comment: 35 pages, 3 figure
The clustering of ultra-high energy cosmic rays and their sources
The sky distribution of cosmic rays with energies above the 'GZK cutoff'
holds important clues to their origin. The AGASA data, although consistent with
isotropy, shows evidence for small-angle clustering, and it has been argued
that such clusters are aligned with BL Lacertae objects, implicating these as
sources. It has also been suggested that clusters can arise if the cosmic rays
come from the decays of very massive relic particles in the Galactic halo, due
to the expected clumping of cold dark matter. We examine these claims and show
that both are in fact not justified.Comment: 13 pages, 8 figures, version in press at Phys. Rev.
Dynamical mean-field approach to materials with strong electronic correlations
We review recent results on the properties of materials with correlated
electrons obtained within the LDA+DMFT approach, a combination of a
conventional band structure approach based on the local density approximation
(LDA) and the dynamical mean-field theory (DMFT). The application to four
outstanding problems in this field is discussed: (i) we compute the full
valence band structure of the charge-transfer insulator NiO by explicitly
including the p-d hybridization, (ii) we explain the origin for the
simultaneously occuring metal-insulator transition and collapse of the magnetic
moment in MnO and Fe2O3, (iii) we describe a novel GGA+DMFT scheme in terms of
plane-wave pseudopotentials which allows us to compute the orbital order and
cooperative Jahn-Teller distortion in KCuF3 and LaMnO3, and (iv) we provide a
general explanation for the appearance of kinks in the effective dispersion of
correlated electrons in systems with a pronounced three-peak spectral function
without having to resort to the coupling of electrons to bosonic excitations.
These results provide a considerable progress in the fully microscopic
investigations of correlated electron materials.Comment: 24 pages, 14 figures, final version, submitted to Eur. Phys. J. for
publication in the Special Topics volume "Cooperative Phenomena in Solids:
Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom
Evidence for Shock Acceleration and Intergalactic Magnetic Fields in a Large-Scale Filament of Galaxies ZwCl 2341.1+0000
We report the discovery of large-scale diffuse radio emission from what
appears to be a large-scale filamentary network of galaxies in the region of
cluster ZwCl 2341.1+0000, and stretching over an area of at least Mpc in diameter. Multicolour CCD observations yield photometric
redshifts indicating that a significant fraction of the optical galaxies in
this region is at a redshift of z=0.3. This is supported by spectroscopic
measurements of 4 galaxies in the SDSS survey at a mean z=0.27. We present VLA
images at 20 cm (NVSS) and 90 cm wavelengths, showing the detailed radio
structure of the filaments. Comparison with the VLA high resolution FIRST radio
survey shows that the diffuse emission is not due to known individual point
sources. The diffuse radio-emission has a spectral index , and is most likely synchrotron emission from relativistic charged
particles in an inter-galactic magnetic field. Furthermore, this optical/radio
structure is detected in X-rays by the ROSAT all-sky survey. It has a 0.1--2.4
keV luminosity of about erg s and shows an extended highly
non-relaxed morphology. These observations suggest that ZwCl 2341.1+0000 is
possibly a proto-cluster of galaxies in which we are witnessing the process of
structure formation. We show (both analytically and by numerical simulations)
that the energetics of accretion shocks generated in forming large-scale
structures are sufficient to produce enough high energy cosmic-ray (CR)
electrons required to explain the observed radio emission, provided a magnetic
field of strength of about 1 micro Gauss is present there.Thus it is the first
evidence of cosmic-ray particle acceleration and magnetic fields occuring on a
super-cluster scale. (Abridged)Comment: Replaced with the published version. The published paper can be
accessed from http://www.elsevier.com/gej-ng/10/33/29/71/56/53/article.htm
Organic Superconductors: when correlations and magnetism walk in
This survey provides a brief account for the start of organic
superconductivity motivated by the quest for high Tc superconductors and its
development since the eighties'. Besides superconductivity found in 1D organics
in 1980, progresses in this field of research have contributed to better
understand the physics of low dimensional conductors highlighted by the wealth
of new remarkable properties. Correlations conspire to govern the low
temperature properties of the metallic phase. The contribution of
antiferromagnetic fluctuations to the interchain Cooper pairing proposed by the
theory is borne out by experimental investigations and supports
supercondutivity emerging from a non Fermi liquid background. Quasi one
dimensional organic superconductors can therefore be considered as simple
prototype systems for the more complex high Tc materials.Comment: 41 pages, 21 figures to be published in Journal of Superconductivity
and Novel Magnetis
Elucidation of active site residues of Arabidopsis thaliana flavonol synthase provides a molecular platform for engineering flavonols
10.1016/j.phytochem.2007.07.006Phytochemistry69166-7