1,721,055 research outputs found
Phase separation in iron chalcogenide superconductor Rb0.8+xFe1.6+ySe2 as seen by Raman light scattering and band structure calculations
No full textWe report Raman light scattering in the phase separated superconducting single crystal Rb0.77Fe1.61Se2 with Tc = 32 K over a wide temperature region 3-500 K. The observed phonon lines from the majority vacancy ordered Rb2Fe4Se5 (245) antiferromagnetic phase with TN = 525 K demonstrate modest anomalies in the frequency, intensity and halfwidth at the superconductive phase transition. We identify phonon lines from the minority compressed RbδFe2Se2 (122) conductive phase. The superconducting gap with dx 2-y 2 symmetry has been detected in our spectra. In the range 0-600 cm-1 we observe a weak but highly polarized B1g-type background which becomes well-structured upon cooling. A possible magnetic or multiorbital origin of this background is discussed. We argue that the phase separation in M0.8+xFe1.6+ySe2 is of pure magnetic origin. It occurs below the Néel temperature when the magnetic moment of iron reaches a critical value. We state that there is a spacer between the majority 245 and minority 122 phases. Using ab initio spin-polarized band structure calculations we demonstrate that the compressed vacancy ordered Rb2Fe4Se5 phase can be conductive and therefore may serve as a protective interface spacer between the purely metallic RbδFe2Se2 phase and the insulating Rb2Fe4Se5 phase providing percolative Josephson-junction like superconductivity all throughout of Rb0.8+xFe1.6+ySe2. Our lattice dynamics calculations show significant differences in the phonon spectra of the conductive and insulating Rb2Fe4Se5phases. PACS: 78.30.-j Infrared and Raman spectra; 74.25.Jb Electronic structure (photoemission, etc.); 74.25.Kc Phonons; 74.70.Xa Pnictides and chalcogenides. © Yu. Pashkevich, V. Gnezdilov, P. Lemmens, T. Shevtsova, A. Gusev, K. Lamonova, D. Wulferding, S. Gnatchenko, E. Pomjakushina, and K. Conder, 2016 Published by AIP Publishing011sciescopu
Relation between cuprate superconductivity and magnetism: A Raman study of (CaLa)1(BaLa)2Cu3 Oy
Get PDFWe present an investigation of charge-compensated antiferromagnetic (CaxLa1.x)(Ba1.75.xLa0.25+x)Cu3Oy
single crystals using Raman scattering as well as muon spin rotation. In this system the parameter x controls
the Cu-O-Cu superexchange interaction via bond distances and buckling angles. The oxygen content y controls
the charge doping. In the absence of doping the two-magnon peak position is directly proportional to the
superexchange strength J .We find that both x and y affect the peak position considerably. The N´eel temperature
determined from muon spin rotation on the same samples independently confirms the strong dependence of the
magnetic interaction on x and y. We find a considerable increase in the maximum superconducting transition
temperature T max
c with J . This is strong evidence of the importance of orbital overlap to superconductivity in this
family of cuprates.1551sciescopu
Lattice and orbital fluctuations in TiPO4
Get PDFIn the s = 1/2 antiferromagnetic spin chain material TiPO4, the formation of a spin gap takes place in a
two-step process with two characteristic temperatures, T
∗ = 111 K and TSP = 74 K. We observe an unusual
lattice dynamics over a large temperature regime as well as evidence for an orbital instability preceding the
spin-Peierls transition. We relate different intrachain exchange interactions of the high temperature compared
to the spin-Peierls phase to a modification of the orbital ordering pattern. In particular, our observation of a
high-energy excitation of mixed electronic and lattice origin suggests an exotic dimerization process different
from other spin-Peierls materials.1221sciescopu
Experimental signatures of nodeless multiband superconductivity in a 2H-Pd 0.08 TaSe 2 single crystal
No full textAbstract In order to understand the superconducting gap nature of a 2H-Pd 0.08 TaSe 2 single crystal with T c = 3.13 K , in-plane thermal conductivity κ , in-plane London penetration depth λ L , and the upper critical fields H c 2 have been investigated. At zero magnetic field, it is found that no residual linear term κ 0 / T exists and λ L follows a power-law T n (T: temperature) with n = 2.66 at T ≤ 1 3 T c , supporting nodeless superconductivity. Moreover, the magnetic-field dependence of κ 0 /T clearly shows a shoulder-like feature at a low field region. The temperature dependent H c 2 curves for both in-plane and out-of-plane field directions exhibit clear upward curvatures near T c , consistent with the shape predicted by the two-band theory and the anisotropy ratio between the H c 2 (T) curves exhibits strong temperature-dependence. All these results coherently suggest that 2H-Pd 0.08 TaSe 2 is a nodeless, multiband superconductor
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
Local characterization of a heavy-fermion superconductor via sub-Kelvin magnetic force microscopy
No full textUsing magnetic force microscopy operating at sub-Kelvin temperatures, we characterize the heavy fermion superconductor CeCoIn5. We pinpoint the absolute London penetration depth of lambda ( 0 ) = 435 +/- 20 nm and report its temperature dependence, which is closely linked to the symmetry of the superconducting gap. In addition, we directly measure the pinning force of individual Abrikosov vortices and estimate the critical current density of j c = 9 x 10 4A/cm(2). In contrast to the related, well-established tunnel diode oscillator technique, our method is capable of resolving inhomogeneities locally on the micrometer scale at ultra-low temperature.11Nsciescopu
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
One-ninth magnetization plateau stabilized by spin entanglement in a kagome antiferromagnet
No full textThe spin-1/2 antiferromagnetic Heisenberg model on a kagome lattice is geometrically frustrated, which is expected to promote the formation of many-body quantum entangled states. The most sought-after among these is the quantum spin-liquid phase, but magnetic analogues of liquid, solid and supersolid phases may also occur, producing fractional plateaus in the magnetization. Here, we investigate the experimental realization of these predicted phases in the kagome material YCu3(OD)6+xBr3−x (x ≈ 0.5). By combining thermodynamic and Raman spectroscopic techniques, we provide evidence for fractionalized spinon excitations and observe the emergence of a 1/9 magnetization plateau. These observations establish YCu3(OD)6+xBr3−x as a model material for exploring the 1/9 plateau phase. © 2024, The Author(s), under exclusive licence to Springer Nature Limited.11Nsciescopu
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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