185 research outputs found
Layer-resolved magnetic exchange interactions of surfaces of late 3d elements: effects of electronic correlations
We present the results of an ab initio study of magnetic properties of Fe, Co
and Ni surfaces. In particular, we discuss their electronic structure and
magnetic exchange interactions (Jij), as obtained by means of a combination of
density functional theory and dynamical mean-field theory. All studied systems
have a pronounced tendency to ferromagnetism both for bulk and surface atoms.
The presence of narrow-band surface states is shown to enhance the magnetic
moment as well as the exchange couplings. The most interesting results were
obtained for the Fe surface where the atoms have a tendency to couple
antiferromagnetically with each other. This interaction is relatively small,
when compared to interlayer ferromagnetic interaction, and strongly depends on
the lattice parameter. Local correlation effects are shown to lead to strong
changes of the overall shape of the spectral functions. However, they seem to
not play a decisive role on the overall picture of the magnetic couplings
studied here. We have also investigated the influence of correlations on the
spin and orbital moments of the bulk-like and surface atoms. We found that
dynamical correlations in general lead to enhanced values of the orbital
moment.Comment: 13 pages, 12 figure
Supercurrent transferring through c-axis cuprate Josephson junctions with thick normal-metal-bridge
With simple but exactly solvable model, we investigate the supercurrent
transferring through the c-axis cuprate superconductor-normal
metal-superconductor junctions with the clean normal metal much thicker than
its coherence length. It is shown that the supercurrent as a function of
thickness of the normal metal decreases much slower than the exponential
decaying expected by the proximity effect. The present result may account for
the giant proximity effect observed in the c-axis cuprate SNS junctions.Comment: 6 pages, 4 figure
Proximity Effect Enhancement Induced by Roughness of SN Interface
Critical temperature reduction is considered for a thin film of
a layered superconductor (S) with a rough surface covered by a thick layer of a
normal metal (N). The roughness of the SN interface increases the penetration
of electrons from the normal metal into the superconductor and leads to an
enhancement of the proximity effect. The value of induced by the
roughness of the SN interface can be much higher than for a film
with a plain surface for an extremely anisotropic layered superconductor with
the coherence lengths .Comment: 2 page
Magnetism and exchange interaction of small rare-earth clusters; Tb as a representative
Here we follow, both experimentally and theoretically, the development of
magnetism in Tb clusters from the atomic limit, adding one atom at a time. The
exchange interaction is, surprisingly, observed to drastically increase
compared to that of bulk, and to exhibit irregular oscillations as a function
of the interatomic distance. From electronic structure theory we find that the
theoretical magnetic moments oscillate with cluster size in exact agreement
with experimental data. Unlike the bulk, the oscillation is not caused by the
RKKY mechanism. Instead, the inter-atomic exchange is shown to be driven by a
competition between wave-function overlap of the 5d shell and the on-site
exchange interaction, which leads to a competition between ferromagnetic
double-exchange and antiferromagnetic super-exchange. This understanding opens
up new ways to tune the magnetic properties of rare-earth based magnets with
nano-sized building blocks
Magnetic moments of W 5d in Ca2CrWO6 and Sr2CrWO6 double perovskites
We have investigated the magnetic moment of the W ion in the ferrimagnetic
double perovskites Sr2CrWO6 and Ca2CrWO6 by X-ray magnetic circular dichroism
(XMCD) at the W L(2,3) edges. In both compounds a finite negative spin and
positive orbital magnetic moment was detected. The experimental results are in
good agreement with band-structure calculations for (Sr/Ca)2CrWO6 using the
full-potential linear muffin-tin orbital method. It is remarkable, that the
magnetic ordering temperature, TC, is correlated with the magnetic moment at
the 'non-magnetic' W atom.Comment: accepted for publicatio
High photon energy spectroscopy of NiO: experiment and theory
We have revisited the valence band electronic structure of NiO by means of
hard x-ray photoemission spectroscopy (HAXPES) together with theoretical
calculations using both the GW method and the local density approximation +
dynamical mean-field theory (LDA+DMFT) approaches. The effective impurity
problem in DMFT is solved through the exact diagonalization (ED) method. We
show that the LDA+DMFT method alone cannot explain all the observed structures
in the HAXPES spectra. GW corrections are required for the O bands and Ni-s and
p derived states to properly position their binding energies. Our results
establish that a combination of the GW and DMFT methods is necessary for
correctly describing the electronic structure of NiO in a proper ab-initio
framework. We also demonstrate that the inclusion of photoionization cross
section is crucial to interpret the HAXPES spectra of NiO.We argue that our
conclusions are general and that the here suggested approach is appropriate for
any complex transition metal oxide.Comment: 16 pages, 5 figure
In vitro analysis of phosphorothioate modification of DNA reveals substrate recognition by a multiprotein complex
A wide variety of prokaryotes possess DNA modifications consisting of sequence-specific phosphorothioates (PT) inserted by members of a five-gene cluster. Recent genome mapping studies revealed two unusual features of PT modifications: short consensus sequences and partial modification of a specific genomic site in a population of bacteria. To better understand the mechanism of target selection of PT modifications that underlies these features, we characterized the substrate recognition of the PT-modifying enzymes termed DptC, D and E in a cell extract system from Salmonella. The results revealed that double-stranded oligodeoxynucleotides underwent de novo PT modification in vitro, with the same modification pattern as in vivo, i. e., GpsAAC/GpsTTC motif. Unexpectedly, in these in vitro analyses we observed no significant effect on PT modification by sequences flanking GAAC/GTTC motif, while PT also occurred in the GAAC/GTTC motif that could not be modified in vivo. Hemi-PT DNA also served as substrate of the PT-modifying enzymes, but not single-stranded DNA. The PT-modifying enzymes were then found to function as a large protein complex, with all of three subunits in tetrameric conformations. This study provided the first demonstration of in vitro DNA PT modification by PT-modifying enzymes that function as a large protein complex.National Natural Science Foundation (China) (Grant 31470183)National Natural Science Foundation (China) (Grant 31400029)National Natural Science Foundation (China) (Grant 31170085)National Natural Science Foundation (China) (Grant 30570400)National Natural Science Foundation (China) (Grant 31070058)China. Ministry of Science and Technology (Grant 2012CB721004)China. Ministry of Science and Technology (Grant 2009ZX09501-008)Shanghai Municipal Council of Science and Technology (Shanghai Pujiang Program Grant 12PJD021)China Scholarship CouncilNational Science Foundation (U.S.) (Grant CHE-1019990)National Institute of Environmental Health Sciences (Grant ES002109)Singapore. National Research Foundation (Singapore-MIT Alliance for Research and Technology
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