905 research outputs found
Interacting Electrons, Spin Statistics, and Information Theory
We consider a nearly (or quasi) uniform gas of interacting electrons for which spin statistics play a crucial role. A previously developed procedure, based on the extension of the Levy–Lieb constrained search principle and Monte Carlo sampling of electron configurations in space, allows us to approximate the form of the kinetic-energy functional. For a spinless electron gas, this procedure led to a correlation term, which had the form of the Shannon entropy, but the resulting kinetic-energy functional does not satisfy the Lieb–Thirring inequality, which is rigorous and one of the most general relations regarding the kinetic energy. In this paper, we show that when the fermionic character of the electrons is included via a statistical spin approach, our procedure leads to correlation terms, which also have the form of the Shannon entropy and the resulting kinetic-energy functional does satisfy the Lieb–Thirring inequality. In this way we further strengthen the connection between Shannon entropy and electron correlation and, more generally, between information theory and quantum mechanics
Exchange Splitting and Charge Carrier Spin Polarization in EuO
High quality thin films of the ferromagnetic semiconductor EuO have been
prepared and were studied using a new form of spin-resolved spectroscopy. We
observed large changes in the electronic structure across the Curie and
metal-insulator transition temperature. We found that these are caused by the
exchange splitting of the conduction band in the ferromagnetic state, which is
as large as 0.6 eV. We also present strong evidence that the bottom of the
conduction band consists mainly of majority spins. This implies that doped
charge carriers in EuO are practically fully spin polarized.Comment: 4 pages, 5 figure
Estudo da variabilidade entomopatogênicos nematóides populações (Heterorhabditidae) da Argentina
Entomopathogenic nematodes (EPN) belonging to the Heterorhabditidae family are lethal parasites of soil-dwelling insects. Two species were reported in Argentina: Heterorhabditis argentinensis and Heterorhabditis bacteriophora characterized mainly by morphometric features. In this work a comparative and phylogenetic study between five Heterorhabditis populations from Argentina was conducted to analyze the variability between strains and to evaluate the taxonomic position of Heterorhabditis argentinensis. The PCA analyses of morphometric characters separated the larger juvenile, female and male H. argentinensis from H. bacteriophora populations. The juvenile (IJs) stage provided the clearest separation of Heterorhabditis populations presenting the least variability between strains. The variable L and MBW were highly related to H. argentinensis IJs. Three groups were separated by this stage considering PC1 and PC2: one formed by H. bacteriophora OLI, RIV and RN strains, (isolates from Córdoba and Río Negro province), one for H. bacteriophora VELI strain (Buenos Aires province) and one for H. argentinensis (Santa Fe province). Heterorhabditis bacteriophora VELI and H. argentinensis isolated from regions with more rainfalls and humidity presented larger values for morphometric features. Molecular analyses showed the Argentinian populations (H. bacteriophora VELI strain and H. argentinensis), forming a same clade, with six other H. bacteriophora populations (not from Argentina) with a genetic similarity between them of 99%. Heterorhabditis argentinensis presented one unique nucleotide that was not present in any of the other species of the clade. Considering the results of this study H. argentinensis would be conspecific to H. bacteriophora, constituting a strain with a great morphometric variation where the host and climatic conditions could have influenced on the measurements.Nematóides entomopatogênicos (EPN) pertencentes á família Heterorhabditidae são parasitas letais de insetos que vivem no solo. Duas espécies foram relatados na Argentina: Heterorhabditis argentinensis e Heterorhabditis bacteriophora, caracterizada principalmente por características morfométricas. Neste trabalho um estudo comparativo e filogenética entre cinco populações do Heterorhabditis da Argentina foi conduzido para analisar a variabilidade entre as linhagens e avaliar a posição taxonômica das Heterorhabditis argentinensis. Características morfométricas de Heterorhabditis bacteriophora VELI e H. argentinensis isoladas de regiões com mais chuvas e umidade apresentaram dimensões maiores. Analisa o PCA de personagens morfométricas separou a maior juvenil, feminino e masculino H. argentinensis de H. bacteriophora populações. A fase juvenil (JIs) fornece a mais clara separação de populações Heterorhabditis apresentando a menor variação entre as cepas. A L variável e MBW foram altamente relacionada com H. argentinensis JIs. Três grupos foram separados por esta fase considerando PC1 e PC2: um formado por H. bacteriophora OLI, RIV e estirpes RN, (isolados de Córdoba e província de Rio Negro), um para a estirpe H. bacteriophora VELI (província de Buenos Aires) e um para H. argentinensis (província de Santa Fe). Heterorhabditis bacteriophora VELI e H. argentinensis isolado a partir de regiões com mais chuvas e umidade apresentaram maiores valores para as características morfométricas. A análise molecular mostrou as populações da Argentina (estirpe H. bacteriophora VELI e H. argentinensis), formando um mesmo subtipo, com seis outras populações H. bacteriophora (não da Argentina), com uma similaridade genética entre eles de 99%. Heterorhabditis argentinensis apresentado um único nucleótido que não estava presente em nenhum dos outros espécies do clado. Considerando os resultados deste estudo H. argentinensis seria conspecific a H. bacteriophora, constituindo uma estirpe com uma grande variação morfométrica onde o anfitrião e as condições climáticas podem ter influenciado nas medições.Centro de Estudios Parasitológicos y de Vectore
Estudo da variabilidade entomopatogênicos nematóides populações (Heterorhabditidae) da Argentina
Entomopathogenic nematodes (EPN) belonging to the Heterorhabditidae family are lethal parasites of soil-dwelling insects. Two species were reported in Argentina: Heterorhabditis argentinensis and Heterorhabditis bacteriophora characterized mainly by morphometric features. In this work a comparative and phylogenetic study between five Heterorhabditis populations from Argentina was conducted to analyze the variability between strains and to evaluate the taxonomic position of Heterorhabditis argentinensis. The PCA analyses of morphometric characters separated the larger juvenile, female and male H. argentinensis from H. bacteriophora populations. The juvenile (IJs) stage provided the clearest separation of Heterorhabditis populations presenting the least variability between strains. The variable L and MBW were highly related to H. argentinensis IJs. Three groups were separated by this stage considering PC1 and PC2: one formed by H. bacteriophora OLI, RIV and RN strains, (isolates from Córdoba and Río Negro province), one for H. bacteriophora VELI strain (Buenos Aires province) and one for H. argentinensis (Santa Fe province). Heterorhabditis bacteriophora VELI and H. argentinensis isolated from regions with more rainfalls and humidity presented larger values for morphometric features. Molecular analyses showed the Argentinian populations (H. bacteriophora VELI strain and H. argentinensis), forming a same clade, with six other H. bacteriophora populations (not from Argentina) with a genetic similarity between them of 99%. Heterorhabditis argentinensis presented one unique nucleotide that was not present in any of the other species of the clade. Considering the results of this study H. argentinensis would be conspecific to H. bacteriophora, constituting a strain with a great morphometric variation where the host and climatic conditions could have influenced on the measurements.Nematóides entomopatogênicos (EPN) pertencentes á família Heterorhabditidae são parasitas letais de insetos que vivem no solo. Duas espécies foram relatados na Argentina: Heterorhabditis argentinensis e Heterorhabditis bacteriophora, caracterizada principalmente por características morfométricas. Neste trabalho um estudo comparativo e filogenética entre cinco populações do Heterorhabditis da Argentina foi conduzido para analisar a variabilidade entre as linhagens e avaliar a posição taxonômica das Heterorhabditis argentinensis. Características morfométricas de Heterorhabditis bacteriophora VELI e H. argentinensis isoladas de regiões com mais chuvas e umidade apresentaram dimensões maiores. Analisa o PCA de personagens morfométricas separou a maior juvenil, feminino e masculino H. argentinensis de H. bacteriophora populações. A fase juvenil (JIs) fornece a mais clara separação de populações Heterorhabditis apresentando a menor variação entre as cepas. A L variável e MBW foram altamente relacionada com H. argentinensis JIs. Três grupos foram separados por esta fase considerando PC1 e PC2: um formado por H. bacteriophora OLI, RIV e estirpes RN, (isolados de Córdoba e província de Rio Negro), um para a estirpe H. bacteriophora VELI (província de Buenos Aires) e um para H. argentinensis (província de Santa Fe). Heterorhabditis bacteriophora VELI e H. argentinensis isolado a partir de regiões com mais chuvas e umidade apresentaram maiores valores para as características morfométricas. A análise molecular mostrou as populações da Argentina (estirpe H. bacteriophora VELI e H. argentinensis), formando um mesmo subtipo, com seis outras populações H. bacteriophora (não da Argentina), com uma similaridade genética entre eles de 99%. Heterorhabditis argentinensis apresentado um único nucleótido que não estava presente em nenhum dos outros espécies do clado. Considerando os resultados deste estudo H. argentinensis seria conspecific a H. bacteriophora, constituindo uma estirpe com uma grande variação morfométrica onde o anfitrião e as condições climáticas podem ter influenciado nas medições.Centro de Estudios Parasitológicos y de Vectore
Evidence of orbital reconstruction at interfaces in La0.67Sr0.33MnO3 films
Electronic properties of transition metal oxides at interfaces are influenced
by strain, electric polarization and oxygen diffusion. Linear dichroism (LD)
x-ray absorption, diffraction, transport and magnetization on thin
La0.7Sr0.3MnO3 films, allow identification of a peculiar universal interface
effect. We report the LD signature of preferential 3d-eg(3z2-r2) occupation at
the interface, suppressing the double exchange mechanism. This surface orbital
reconstruction is opposite of that favored by residual strain and independent
of dipolar fields, chemical nature of the substrate and capping.Comment: 13 pages, 5 figure
Evolution of magnetic phases and orbital occupation in (SrMnO3)n/(LaMnO3)2n superlattices
The magnetic and electronic modifications induced at the interfaces in
(SrMnO)/(LaMnO) superlattices have been investigated
by linear and circular magnetic dichroism in the Mn L x-ray absorption
spectra. Together with theoretical calculations, our data demonstrate that the
charge redistribution across interfaces favors in-plane ferromagnetic (FM)
order and orbital occupation, in agreement with the
average strain. Far from interfaces, inside LaMnO, electron localization
and local strain favor antiferromagnetism (AFM) and
orbital occupation. For the high density of interfacial planes ultimately
leads to dominant FM order forcing the residual AFM phase to be in-plane too,
while for the FM layers are separated by AFM regions having
out-of-plane spin orientation.Comment: accepted for publication as a Rapid Communication in Physical Review
Directly characterizing the relative strength and momentum dependence of electron-phonon coupling using resonant inelastic x-ray scattering
The coupling between lattice and charge degrees of freedom in condensed
matter materials is ubiquitous and can often result in interesting properties
and ordered phases, including conventional superconductivity, charge density
wave order, and metal-insulator transitions. Angle-resolved photoemission
spectroscopy and both neutron and non-resonant x-ray scattering serve as
effective probes for determining the behavior of appropriate, individual
degrees of freedom -- the electronic structure and lattice excitation, or
phonon dispersion, respectively. However, each provides less direct information
about the mutual coupling between the degrees of freedom, usual through
self-energy effects, which tend to renormalize and broaden spectral features
precisely where the coupling is strong, impacting ones ability to quantitively
characterize the coupling. Here we demonstrate that resonant inelastic x-ray
scattering, or RIXS, can be an effective tool to directly determine the
relative strength and momentum dependence of the electron-phonon coupling in
condensed matter systems. Using a diagrammatic approach for an 8-band model of
copper oxides, we study the contributions from the lowest order diagrams to the
full RIXS intensity for a realistic scattering geometry, accounting for matrix
element effects in the scattering cross-section as well as the momentum
dependence of the electron-phonon coupling vertex. A detailed examination of
these maps offers a unique perspective into the characteristics of
electron-phonon coupling, which complements both neutron and non-resonant x-ray
scattering, as well as Raman and infrared conductivity.Comment: 10 pages, 10 figure
Multiple double-exchange mechanism by Mn-doping in manganite compounds
Double-exchange mechanisms in REAEMnO manganites (where
RE is a trivalent rare-earth ion and AE is a divalent alkali-earth ion) relies
on the strong exchange interaction between two Mn and Mn ions
through interfiling oxygen 2p states. Nevertheless, the role of RE and AE ions
has ever been considered "silent" with respect to the DE conducting mechanisms.
Here we show that a new path for DE-mechanism is indeed possible by partially
replacing the RE-AE elements by Mn-ions, in La-deficient
LaMnO thin films. X-ray absorption spectroscopy demonstrated
the relevant presence of Mn ions, which is unambiguously proved to be
substituted at La-site by Resonant Inelastic X-ray Scattering. Mn is
proved to be directly correlated to the enhanced magneto-transport properties
because of an additional hopping mechanism trough interfiling Mn-ions,
theoretically confirmed by calculations within the effective single band model.
The very idea to use Mn both as a doping element and an ions
electronically involved in the conduction mechanism, has never been foreseen,
revealing a new phenomena in transport properties of manganites. More
important, such a strategy might be also pursed in other strongly correlated
materials.Comment: 6 pages, 5 figure
Momentum dependence of orbital excitations in Mott-insulating titanates
High-resolution resonant inelastic x-ray scattering has been used to
determine the momentum dependence of orbital excitations in Mott-insulating
LaTiO and YTiO over a wide range of the Brillouin zone. The data are
compared to calculations in the framework of lattice-driven and
superexchange-driven orbital ordering models. A superexchange model in which
the experimentally observed modes are attributed to two-orbiton excitations
yields the best description of the data.Comment: to appear in PR
Magnetic excitations in stripe-ordered LaBaCuO studied using resonant inelastic x-ray scattering
The charge and spin correlations in LaBaCuO (LBCO
1/8) are studied using Cu edge resonant inelastic x-ray scattering
(RIXS). The static charge order (CO) is observed at a wavevector of
and its charge nature confirmed by measuring the dependence of this peak on the
incident x-ray polarization. The paramagnon excitation in LBCO 1/8 is then
measured as it disperses through the CO wavevector. Within the experimental
uncertainty no changes are observed in the paramagnon due to the static CO, and
the paramagnon seems to be similar to that measured in other cuprates, which
have no static CO. Given that the stripe correlation modulates both the charge
and spin degrees of freedom, it is likely that subtle changes do occur in the
paramagnon due to CO. Consequently, we propose that future RIXS measurements,
realized with higher energy resolution and sensitivity, should be performed to
test for these effects.Comment: 5 pages, 4 figure
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