1,720,960 research outputs found
Doped kagome system as exotic superconductor
No full textA Chern-Simons theory for the doped spin-1/2 kagome system is constructed, from which it is shown that the system is an exotic superconductor that breaks time-reversal symmetry. It is also shown that the system carries minimal vortices of flux hc/4e (as opposed to the usual hc/2e in conventional superconductors) and contains fractional quasiparticles (including fermionic quasiparticles with semionic mutual statistics and spin-1/2 quasiparticles with bosonic self-statistics) in addition to the usual spin-1/2 fermionic Bogoliubov quasiparticles. Two Chern-Simons theories—one with an auxiliary gauge field kept and one with the auxiliary field and a redundant matter field directly eliminated—are presented and shown to be consistent with each other.National Science Foundatio
Proposal for detecting spin-chirality terms in Mott insulators via resonant inelastic x-ray scattering
No full textWe consider the question of whether resonant inelastic x-ray scattering (RIXS) can be used to detect many-body excitations that are coupled to the spin-chirality terms S[subscript i]·(S[subscript j]×S[subscript k]) in a Mott insulator. We find that while the spin-chirality terms are in general absent in the usual experimental setups of RIXS, there are prospects of realizing such terms if one considers instead the scattering near a pre-edge. We then perform detailed analyses for the square and the kagome lattices, and brief analyses for the triangular and the honeycomb lattices, in which we show that the spin-chirality terms are indeed present in all the above lattices, but that they occur at a higher order in our expansion for the kagome and the honeycomb lattices. The merit of using RIXS in addition to Raman spectroscopy to detect excitations that are coupled to the spin-chirality terms is also briefly discussed in the context of the emergent gauge boson in the U(1) Dirac spin liquid.National Science Foundation (U.S.) (Grant No. NSF PHY05-51164)United States. Dept. of Energy (Grant No. DE-FG02-03ER46076
Magnetism and Mott transition: A slave-rotor study
No full textMotivated by the debate of the spin-density-wave (SDW) versus local-moment (LM) picture in the iron-based superconducting (FeSC) materials, we consider a two-band orbital-symmetric Hubbard model in which there is robust Fermi surface nesting at (Pi,0). We obtain the phase diagram of such system by a mean-field slave-rotor approach, in which theFermi surface nesting and the SDW order are explicitly taken into account via a natural separation of scale between the Hund’s coupling and the Coulomb interaction. We find that for a sizeable range of Hund’s coupling the Mott transition acquires a strong first-order character, but there also exists a small range of stronger Hund’s coupling in which an enhancement of magnetization can be observed on the SDW side. We interpret the former scenario as one in which a sharp distinction can bedrawn between the LM and the SDW picture, and the latter scenario as one in which signs of LM physics begin to develop in the metallic phase. It is tempting to suggest that some FeSC materials are in the vicinity of the latter scenario.United States. Dept. of Energy (grant DE-FG02-03ER46076)National Science Foundation (U.S.) (grant PHY05-51164
Spontaneous Spin Ordering of a Dirac Spin Liquid in a Magnetic Field
No full textThe Dirac spin liquid was proposed to be the ground state of the spin-1/2 kagomé antiferromagnets. In a magnetic field B, we show that the state with Fermi pocket is unstable to the Landau level (LL) state. The LL state breaks the spin rotation around the axis of the magnetic field. We find that the LL state has an in-plane 120° q=0 magnetization M which scales with the external field M∼B[subscript α], where α is a universal number of the Dirac spin liquid. We discuss the related experimental implications which can be used to detect the possible Dirac spin liquid phase in herbertsmithite ZnCu[subscript 3](OH)[subscript 6]C[subscript l2].National Science Foundatio
Raman signature of the U(1) Dirac spin-liquid state in the spin-1/2 kagome system
No full textWe followed the Shastry-Shraiman formulation of Raman scattering in Hubbard systems and considered the Raman intensity profile in the spin-1/2 “perfect” kagome lattice herbertsmithite ZnCu[subscript 3](OH)[subscript 6]Cl[subscript 2], assuming the ground state is well-described by the U(1) Dirac spin-liquid state. In the derivation of the Raman T matrix, we found that the spin-chirality term appears in the A[subscript 2g] channel in the kagome lattice at the t4/(omega i−U)3 order, but (contrary to the claims by Shastry and Shraiman) vanishes in the square lattice to that order. In the ensuing calculations on the spin-1/2 kagome lattice, we found that the Raman intensity profile in the Eg channel is invariant under an arbitrary rotation in the kagome plane, and that in all (A[subscript 1g], E[subscript g], and A[subscript 2g]) symmetry channels the Raman intensity profile contains broad continua that display power-law behaviors at low energy, with exponent approximately equal to 1 in the A[subscript 2g] channel and exponent approximately equal to 3 in the E[subscript g] and the A[subscript 1g] channels. For the A[subscript 2g] channel, the Raman profile also contains a characteristic 1/omega singularity, which arose in our model from an excitation of the emergent U(1) gauge field.National Science Foundation (Grant No. DMR-0804040
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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