3,084 research outputs found
Genesis of Coexisting Itinerant and Localized Electrons in Iron Pnictides
No full textWe show how the general features of the electronic structure of the Fe-based high-Tc superconductors are a natural setting for a selective localization of the conduction electrons to arise. Slave-spin and dynamical mean-field calculations support this picture and allow for a comparison of the magnetic properties with experiments. RI Capone, Massimo/A-7762-2008; de' Medici, Luca/H-5071-201
Commensurate versus incommensurate spin ordering in the triangular Hubbard model
No full textThe presence of incommensurate spin structures in the half-filled triangular Hubbard model, where frustration leads to a competition among different magnetic phases, is investigated using both the slave-boson technique, and exact diagonalization of finite clusters. We also investigate the metal-insulator transition which, due to the lack of perfect nesting, takes place at a finite value of U. Within the slave-boson approach. as the interaction grows the paramagnetic metal turns into a metallic phase with incommensurate spiral ordering. Increasing further the interaction, a linear spin-density-wave is stabilized, and finally for strong coupling the latter phase undergoes a first-order transition towards an antiferromagnetic insulator. No trace of the intermediate phases is instead found in the exact diagonalization results. RI Capone, Massimo/A-7762-200
«Preferirebbe buttar via il nome». L’evasione dal principium individuationis del nome e dall’identità in ‘Rubè’ di Borgese
No full textThe paper highlights the remarkable pregnancy, in thematic, ideological, formal and
even structural terms, of names in Rubè (1921), a novel by Giuseppe Antonio Borgese, focusing on
the troublesome relationship that the main character Filippo Rubè establishes with them, leading
to an identity crisis. Capone identifies five modes of using names in Rubè: the escape from the principium
individuationis of the name as an ideological breakout from the chains of a fixed identity; the
intentional modifications of his name made by Rubè in order to avoid his registry and social identity
and, thus, to be able to escape from the duties of ordinary life; the change of the names of the women
loved by Filippo; some irreversible plot twists brought about by proper names; the inability to give
adequate names to blurred feelings. By the analysis of these uses, the author points out how many
times in Rubè not just nomina sunt consequentia rerum, but res sunt consequentia nominum as well
Solving the dynamical mean-field theory at very low temperatures using the Lanczos exact diagonalization
No full textWe present an efficient method to solve the impurity Hamiltonians involved in dynamical mean-field theory at low but finite temperature based on the extension of the Lanczos algorithm from ground state properties alone to excited states. We test the approach on the prototypical Hubbard model and find extremely accurate results from T=0 up to relatively high temperatures up to the scale of the critical temperature for the Mott transition. The algorithm substantially decreases the computational effort involved in finite temperature calculations. RI Capone, Massimo/A-7762-2008; de' Medici, Luca/H-5071-2011; Georges, Antoine/H-4855-201
Phase separation in the 2D Hubbard model: a fixed-node quantum Monte Carlo study
No full textFixed-node Green's-function Monte Carlo calculations have been performed for very large 16x16 two-dimensional Hubbard lattices, large interaction strengths U=10,20, and 40, and many (15 similar to 20) densities between empty and half-filling. The nodes were fixed by a simple Slater-Gutzwiller trial wave function. For each value of U we obtained a sequence of ground-state energies which is consistent with the possibility of a phase separation close to half-filling, with a hole density in the hole-rich phase which is a decreasing function of U. The energies suffer, however, from a fixed-node bias: more accurate nodes are needed to confirm this picture. Our extensive numerical results and their test against size, shell, shape, and boundary-condition effects also suggest that phase separation is quite a delicate issue, on which simulations based on smaller lattices than considered here are unlikely to give reliable predictions. RI Capone, Massimo/A-7762-2008; Guidoni, Leonardo/G-3759-201
Tecnica e rappresentazione. L'essere umano come estensione del media digitale
No full textL'’articolo propone una riflessione sulle tecnologie che inscriva i media digitali all’interno del rapporto coestensivo fra antropogenesi e tecnogenesi. Il ruolo costitutivo della tecnica, nel lungo percorso dell’uomo verso l’acquisizione di una mente rappresentativa, viene illustrato speculativamente, ricorrendo alla filosofia della tecnica di Heidegger, ed empiricamente facendo riferimento alla material engagement theory nel contesto degli studi di archeologia della mente. Nelle conclusioni illustreremo come i media digitali non si discostino da quella che Heidegger definisce l’essenza della tecnica moderna, ma che anzi reiterino quel destino impositivo invertendo la relazione fra media e soggetto, facendo di quest’ultimo una risorsa epistemica fondamentale per la realizzazione di una scienza algoritmica
Orbital-Selective Mott Transition out of Band Degeneracy Lifting
No full textWe outline a general mechanism for orbital-selective Mott transition, the coexistence of both itinerant and localized conduction electrons, and show how it can take place in a wide range of realistic situations, even for bands of identical width and correlation, provided a crystal field splits the energy levels in manifolds with different degeneracies and the exchange coupling is large enough to reduce orbital fluctuations. The mechanism relies on the different kinetic energy in manifolds with different degeneracy. This phase has Curie-Weiss susceptibility and non-Fermi-liquid behavior, which disappear at a critical doping, all of which is reminiscent of the physics of the pnictides. RI Dai, Xi/C-4236-2008; Capone, Massimo/A-7762-2008; de' Medici, Luca/H-5071-201
2.1. parte seconda
No full text2.1 : parte seconda / Gaetano Capone Braga. - Padova : CEDAM, 1942
Dedica manoscritta dell\u27autore: per affettuoso ricordo degli anni lontani / G. Capone
https://galileodiscovery.unipd.it/discovery/fulldisplay?context=L&vid=39UPD_INST:VU1&search_scope=MyInst_and_CI&tab=Everything&docid=alma99001275094020604
Antiferromagnetism and the gap of a Mott insulator: Results from analytic continuation of the self-energy
No full textDirect analytic continuation of the self-energy is used to determine the effect of antiferromagnetic ordering on the spectral function and optical conductivity of a Mott insulator. Comparison of several methods shows that the most robust estimation of the gap value is obtained by use of the real part of the continued self-energy in the quasiparticle equation within the single-site dynamical mean-field theory of the two-dimensional square lattice Hubbard model, where, for a U that is slightly greater than the Mott critical value, antiferromagnetism increases the gap by about 80%. RI Capone, Massimo/A-7762-2008; Wang, Xin/F-5509-2011; de' Medici, Luca/H-5071-2011; Gull, Emanuel/A-2362-201
Optical conductivity and the correlation strength of high-temperature copper-oxide superconductors
No full textSince their discovery in 1986, the high-temperature copper-oxide superconductors have been a central object of study in condensed-matter physics. Their highly unusual properties are widely ( although not universally) believed to be a consequence of electron-electron interactions that are so strong that the traditional paradigms of condensed-matter physics do not apply: instead, entirely new concepts and techniques are required to describe the physics. In particular, the superconductivity is obtained by adding carriers to insulating 'parent compounds'. These parent compounds have been identified(1) as 'Mott' insulators, in which the lack of conduction arises from anomalously strong electron-electron repulsion. The unusual properties of Mott insulators are widely(2) believed to be responsible for the high-temperature superconductivity. Here, we present a comparison of new theoretical calculations and published(3-8) optical conductivity measurements, which challenges this belief. The analysis indicates that the correlation strength in the cuprates is not as strong as previously believed, in particular that the materials are not properly regarded as Mott insulators. Rather, antiferromagnetism seems to be necessary to obtain the insulating state. By implication, antiferromagnetism is essential to the properties of the doped metallic and superconducting state as well. RI Capone, Massimo/A-7762-2008; de' Medici, Luca/H-5071-201
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