1,721,306 research outputs found
High-pressure structure and electronic transport in hole-doped La3/4Ca1/4MnO3 perovskites
No full textTheoretical analysis of x-ray-absorption near-edge fine structure at the O and metal K edges of LaFeO3 and LaCoO3
No full textLocal structure of hole-doped manganites: influence of temperature and applied magnetic field
No full textElectron and hole doping in the relativistic Mott insulator Sr2IrO4: a first-principles study using band unfolding technique
No full textWe study the effects of dilute La and Rh substitutional doping on the electronic structure of the relativistic Mott
insulator Sr 2 IrO 4 using fully relativistic and magnetically noncollinear density functional theory with the inclusion
of an on-site Hubbard U . To model doping effects, we have adopted the supercell approach, that allows for a
realistic treatment of structural relaxations and electronic effects beyond a purely rigid band approach. By means of
the band unfolding technique we have computed the spectral function and constructed the effective band structure
and Fermi surface (FS) in the primitive cell, which are readily comparable with available experimental data. Our
calculations clearly indicate that La and Rh doping can be interpreted as effective electron and (fractional) hole
doping, respectively. We found that both electron and hole doping induce an insulating-to-metal transition (IMT)
but with different characteristics. In Sr 2−x La x IrO 4 the IMT is accompanied by a moderate renormalization of the
electronic correlation substantiated by a reduction of the effective on-site Coulomb repulsion U − J from 1.6 eV
(x = 0) to 1.4 eV (metallic regime of x = 12.5%). The progressive closing of the relativistic Mott gap leads to
the emergence of connected elliptical electron pockets at (π/2,π/2) and less intense features at X on the Fermi
surface. The average ordered magnetic moment is slightly reduced upon doping, but the canted antiferromagnetic
state is perturbed on the Ir-O planes located near the La atoms. The substitution of Ir with the nominally isovalent
Rh is accompanied by a substantial hole transfer from the Rh site to the nearest-neighbor Ir sites. This shifts
down the chemical potential, creates almost circular disconnected hole pockets in the FS, and establishes the
emergence of a two-dimensional metallic state formed by conducting Rh planes intercalated by insulating Ir
planes. Finally, our data indicate that hole doping causes a flipping of the in-plane net ferromagnetic moment on
the Rh plane and induces a magnetic transition from the antiferromagnetic (AF)-I to the AF-II ordering
Role of Polar Phonons in the Photo Excited State of Metal Halide Perovskites
Full text linkThe development of high efficiency perovskite solar cells has sparked a multitude of measurements on the optical properties of these materials. For the most studied methylammonium(MA) PbI3 perovskite, a large range (6-55 meV) of exciton binding energies has been reported by various experiments. The existence of excitons at room temperature is unclear. For the MAPbX(3) perovskites we report on relativistic Bethe-Salpeter Equation calculations (GW-BSE). This method is capable to directly calculate excitonic properties from first-principles. At low temperatures it predicts exciton binding energies in agreement with the reported 'large' values. For MAPbI(3), phonon modes present in this frequency range have a negligible contribution to the ionic screening. By calculating the polarization in time from finite temperature molecular dynamics, we show that at room temperature this does not change. We therefore exclude ionic screening as an explanation for the experimentally observed reduction of the exciton binding energy at room temperature and argue in favor of the formation of polarons
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Anisotropic magnetic couplings and structure-driven canted to collinear transitions in Sr2IrO4 by magnetically constrained noncollinear DFT
No full textWe study the canted magnetic state in Sr2IrO4 using fully relativistic density functional theory (DFT) including an on-site Hubbard U correction. A complete magnetic phase diagram with respect to the tetragonal distortion and the rotation of IrO6 octahedra is constructed, revealing the presence of two types of canted to collinear magnetic transitions: a spin-flop transition with increasing tetragonal distortion and a complete quenching of the basal weak ferromagnetic moment below a critical octahedral rotation. Moreover, we put forward a scheme to study the anisotropic magnetic couplings by mapping magnetically constrained noncollinear DFT onto a general spin Hamiltonian. This procedure allows for the simultaneous account and direct control of the lattice, spin, and orbital interactions within a fully ab initio scheme. We compute the isotropic, single site anisotropy and Dzyaloshinskii-Moriya (DM) coupling parameters, and clarify that the origin of the canted magnetic state in Sr2IrO4 arises from the structural distortions and the competition between isotropic exchange and DM interactions
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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