1,721,001 research outputs found
Coulomb-frustrated phase separation phase diagram in systems with short-range negative compressibility
No full textUsing numerical techniques and asymptotic expansions we obtain the phase diagram of a paradigmatic model of Coulomb-frustrated phase separation in systems with negative short-range compressibility. The transition from the homogeneous phase to the inhomogeneous phase is generically first order in isotropic three-dimensional systems except for a critical point. Close to the critical point, inhomogeneities are predicted to form a bcc lattice with subsequent transitions to a triangular lattice of rods and a layered structure. Inclusion of a strong anisotropy allows for second- and first-order transition lines joined by a tricritical point. © 2008 The American Physical Society
Charge-density waves and superconductivity as an alternative to phase separaration in infinite-U Hubbard -Holstein model
No full textWe investigate the density instabilities present in the infinite-U Hubbard-Holstein model both at zero and finite momenta as well as the occurrence of Cooper instabilities with a specific emphasis on the role of long-range Coulomb forces. In carrying out this analysis special attention is devoted to the effects of the strong local e-e interaction on the e-ph coupling and particularly to both the static and dynamic screening processes dressing this coupling. We also clarify under which conditions in strongly correlated electron systems a weak additional interaction, e.g., a phonon-mediated attraction, can give rise to a charge instability. In the presence of long-range Coulomb forces, the frustrated phase separation leads to the formation of incommensurate charge density waves. These instabilities, in turn, lead to strong residual scattering processes between quasiparticles and to superconductivity, thus providing an interesting clue to the interpretation of the physics of the copper oxides
Electronic Thermal Conductivity in Disordered Systems Near the Anderson Transition
No full textThe energy-energy correlation function has been evaluated for a disordered electron system in the absence of the electron-electron interaction ..
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
Thermoelectric power in disordered electronic systems near the Anderson transition
No full textThe number-density-heat-density correlation function for an noninteracting disordered system ..
Pseudogap and (An)isotropic Scattering in the Fluctuating Charge-Density Wave Phase of Cuprates
No full textWe present a general scenario for high-temperature superconducting cuprates, based on the presence of dynamical charge density waves (CDWs) and to the occurrence of a CDW quantum critical point, which occurs, e.g., at doping p ae 0.16 in YBa2Cu3O6 + delta (YBCO). In this framework, the pseudogap temperature T (au) is interpreted in terms of a reduction of the density of states due to incipient CDW and, at lower temperature to the possible formation of incoherent superconducting pairs. The dynamically fluctuating character of CDW accounts for the different temperatures at which the CDW onset revealed by X-ray scattering (T (o n s) (p)), and the static three-dimensional CDW ordering appear. We also investigate the anisotropic character of the CDW-mediated scattering. We find that this is strongly anisotropic only close to the CDW quantum critical point (QCP) at low temperature and very low energy. It rapidly becomes nearly isotropic and marginal-Fermi-liquid-like away from the CDW QCP and at finite (even rather small) energies. This may reconcile the interpretation of Hall measurements in terms of anisotropic CDW scattering (arXiv:1604.07852v1) with recent photoemission experiments Bok, J.M., et al. Sci. Adv. 2, e1501329 (2016)
Infrared Behavior of Interacting Bosons at Zero Temperature
No full textWe exploit the symmetries associated with the stability of the superfluid phase to solve the
long-standing problem of interacting bosons in the presence of a condensate at zero temperature.
Implementation of these symmetries poses strong conditions on the renormalizations that heal
the singularities of perturbation theory. The renormalized theory gives the following: For d . 3
the Bogoliubov quasiparticles as an exact result; for 1 , d # 3 a nontrivial solution with the
exact exponent for the singular longitudinal correlation function, with phonons again as low-lying
excitation
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
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
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