1,721,181 research outputs found
Crystal and Magnetic Structures of La2CoPtO6 Double Perovskite
Get PDFWe investigated the crystal structure and magnetic structure in cobaltite-platinate double perovskite of La2CoPtO6, employing various techniques of X-ray diffraction, neutron diffraction, and the extended X-ray absorption fine structure analysis. It is shown that the crystal symmetry is maintained as P21/n in the temperature range of 0.03 Å) of the Co-Co networks, the system is not subject to spin frustration effect. Details in the magnetic structure are determined; at 12 K, the Co magnetic moment was (0.8, 0, 2.7) Bohr magneton, the magnetic propagation vector was (-0.5, 0, 0.5), and the magnetic symmetry was preferably Δ1(Ag). © 2018 American Chemical Societ
Magnetoelastic octahedral breathing mode in the ferrimagnetic L a2CoIr O6 double perovskite
Get PDFDistortion of transition-metal ion-oxygen octahedra in perovskite structure has been a long standing subject for exploring the physics of charge-orbital-spin-lattice couplings. Recent findings in nickelates or BaBiO3 have suggested that a charge disproportionation in the transition-metal ions can evoke certain cooperative breathing distortions (CBD), constituted by the symmetric expansion and shrinkage of the octahedra in contrast to the Jahn-Teller-type asymmetric distortion. A double perovskite ferrimagnet, La2CoIrO6 bears inherently the charge disproportionation in the cationic sites with Co2+ and Ir4+ sublattices. In light of seeking the clues for the CBD and its coupling to the magnetic order, the crystal structure and magnetic structure of La2CoIrO6 were examined at various temperatures by using neutron diffraction. Structure refinements and mode decomposition analyses revealed that, indeed, a CBD mode exists substantially in La2CoIrO6 while preserving the symmetry of the lattices (P21/n) and the magnetism [Γ1(Ag)]. And more importantly, the magnitude of the symmetric distortion is correlated strongly with the size of the magnetic moment at temperatures below the Curie temperature (∼95 K). This strongly suggests a magnetoelastic coupling of the CBD mode. The order parameters for CBD, e.g., the movement of O1 toward Ir ions at low temperatures, are found to be in a linear-quadratic relationship with the value of the magnetic moment (∼0.002Å/μB2MCo2), manifesting the magnetoelastic CBD in double perovskite. © 2018 American Physical Societ
Keldysh Space Control of Charge Dynamics in a Strongly Driven Mott Insulator
No full text© 2022 American Physical Society.The fate of a Mott insulator under strong low frequency optical driving conditions is a fundamental problem in quantum many-body dynamics. Using ultrafast broadband optical spectroscopy, we measured the transient electronic structure and charge dynamics of an off-resonantly pumped Mott insulator Ca2RuO4. We observe coherent bandwidth renormalization and nonlinear doublon-holon pair production occurring in rapid succession within a sub-100-fs pump pulse duration. By sweeping the electric field amplitude, we demonstrate continuous bandwidth tuning and a Keldysh crossover from a multiphoton absorption to quantum tunneling dominated pair production regime. Our results provide a procedure to control coherent and nonlinear heating processes in Mott insulators, facilitating the discovery of novel out-of-equilibrium phenomena in strongly correlated systems.11Nsciescopu
Hybridized orbital states in spin-orbit coupled 3d-5d double perovskites studied by x-ray absorption spectroscopy
Get PDFWe investigated the orbital hybridization mechanism in 3d-5d double perovskites (DPs) of La2CoIrO6 and La2CoPtO6 using x-ray absorption spectroscopy. It is clearly evidenced by O K-edge and Co K-edge x-ray absorption spectra that the Co 3d orbitals hybridize not only with the half-filled Ir/Pt jeff states but also with the fully empty (unpolarized) Ir/Pt eg states in both DPs. The Co 3d eg-Ir 5d eg hybridization cannot contribute to the ferrimagnetic long-range order in La2CoIrO6 established by spin-selective Co 3d t2g-Ir 5d jeff hybridization through the intermediate oxygen p state but could serve as an origin of paramagnetism. The strengths of such orbital hybridizations were found to be almost invariant to temperature, even far above the Curie temperature, implying persistent paramagnetism against the antiferromagnetic ordering in the spin-orbit entangled 3d-5d DPs. © 2018 American Physical Society1
Abnormal phase flip in the coherent phonon oscillations of Ca2RuO4
Get PDFWe employ an optical pump-probe technique to study coherent phonon oscillations in Ca2RuO4. We find that oscillation amplitude of an Ag symmetric phonon mode is strongly suppressed at 260 K, a putative transition point of orbital ordering. The oscillation also shows a gradual but huge change in its phase, such that the oscillation even flips over with a 180 change across the temperature. Density functional theory calculations indicate that the Ag phonon has an eigenmode of octahedral distortion with conventional tilting along the a axis and antipolar distortion of apical oxygen. Careful inspection of the lattice captures an unusually large antipolar distortion in low-temperature structures, which may play a crucial role for the phase transition at 260 K. ©2018 American Physical Societ
Strong spin-phonon coupling unveiled by coherent phonon oscillations in Ca2RuO4
Get PDF© 2019 American Physical Society. We utilize near-infrared femtosecond pulses to investigate coherent phonon oscillations of Ca2RuO4. The coherent Ag phonon mode of the lowest frequency changes abruptly not only its amplitude but also the oscillation phase as the spin order develops. In addition, the phonon mode shows a redshift entering the magnetically ordered state, which indicates a spin-phonon coupling in the system. Density functional theory calculations reveal that the Ag oscillations result in octahedral tilting distortions, which are exactly in sync with the lattice deformation driven by the magnetic ordering. We suggest that the structural distortions by the spin-phonon coupling can induce the unusual oscillation phase shift between impulsive and displacive type oscillation
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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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