1,721,053 research outputs found
Antiferromagnetic integer-spin chains in a staggered magnetic field: approaching the thermodynamic limit through the density-matrix renormalization group
No full textWe investigate the behavior of antiferromagnetic integer-spin chains in a staggered magnetic field, by means of the density-matrix renormalization group, carefully addressing the role of finite-size effects within the Haldane phase at small fields. In the case of spin S = 2, we determine the dependence of the ground-state energy and magnetization on the external field. in the thermodynamic limit. and show how the peculiar finite-size behavior can be connected with the crossover in the ground state from a spin liquid to a polarized Neel state. RI Capone, Massimo/A-7762-200
Shadow bands, gap and pseudogap in high-Tc superconductors
No full textWithin the framework of the Charge Density Wave Quantum Critical Point (CDW-QCP] scenario for high-Tc superconductors (HTCS) we introduce a model for tight-binding electrons coupled to quasi-critical fluctuations. In the normal state our model reproduces features the Fermi Surface (FS) observed in ARPES measurements on optimality doped Bi2212, such as the anisotropic suppression of spectral weight around the M points of the Brillouin zone. The spectral density is characterized by a transfer of spectral weight from the main quasiparticle peak to dispersing shadow peaks which originate branches of a shadow FS. In the superconducting state our model reproduces the d-wave symmetry of the gap parameter, which results from a balance between small-q attraction and large-q repulsion. The gap parameter is enhanced due to cooperative effects of charge and spin fluctuations
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
Time reversal breaking superconducting state in the phase diagram of the cuprates
No full textWe review and extend a previous study(1) on the symmetry of the superconducting state, stimulated by recent tunneling and Andreev reflection measurements giving robust evidences for the existence of a d(x2-y2) + id(xy) order parameter in the overdoped regime of two different cuprates. Looking for a possible second-order phase transition from a standard d(x2-y2) to a mixed and time reversal breaking state, we confirm the results of our previous analysis on La2-xSrxCuO4. In the case of Y1-yCayBa2Cu3O7-x as well, among all the allowed symmetries, the d(x2-y2) + id(xy) is the most favored one and the unconventional state is likely to occur in a small dome of the phase diagram located in the optimal-overdoped region and at very low temperatures. RI Capone, Massimo/A-7762-200
How Alex Muller's ideas intertwined with the condensed matter theory group of Rome
No full textThe discovery of high-temperature superconductivity in a cuprate by K.A. Muller (AM, hereafter) and J. G. Bednorz triggered an enormous activity all over condensed matter ranging from solid and liquid physics to many body physics and statistical mechanics, as well as a frantic mediatic attention. Besides this, their discovery shaped this field reviving the attention to new and old issues (like, e.g., strong electron-electron correlation, electron-phonon interactions, Fermi liquid theory and its violation, mechanism of superconductivity...). AM accompanied and conditioned for long time this scientific life with his remarks, opinions, and findings. We aim here at recollecting how he followed and stimulated our research activity in all the topics indicated above, to point out how his ideas and our theoretical findings interacted while evolving in both converging or diverging directions
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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