3,533 research outputs found
COMPETIVE EFFECTS ON THE HIGH-PRESSURE PHASE DIAGRAM OF MANGANITES.
No full textRecent infrared absorption measurements performed at different pressures and temperatures on the La0.75Ca0.25MnO3, manganite provided the insulator-to-metal transition temperature T-IM(P), i.e. the P-T phase diagram of the manganite. We report an extended data analysis, by considering in detail pressure and temperature dependence of the observed IR active phonon and of the absorption spectral weights N*. The phonon pressure-dependence, consistently with the P-T phase diagram, indicates the onset of a new localizing interaction above P* = 6-7 GPa. Finally a simple theoretical model will be employed to give a qualitative explanation of the observed high-pressure behavior and to suggest the relevance of the charge-localizing super-exchange magnetic interaction in the very high-pressure regime. Within this framework the asymptotic regime at high pressure is ascribed to the competition between the magnetic super- and double-exchange interactions. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. RI Capone, Massimo/A-7762-200
High-pressure phase diagram in the manganites: a two-site model study
No full textThe pressure dependence of the Curie temperature T-C in manganites, recently studied over a wide pressure range, is not qualitatively accounted for by the quenching of Jahn-Teller distortions, and suggests the occurrence of a new pressure-activated localizing process. On the basis of several high-pressure experiments, the antiferromagnetic (AF) interaction between the core spins has been suggested as a good candidate for such a localizing mechanism. We present a theoretical calculation of T-C based on a two-site double-exchange model with electron-phonon coupling interaction and direct superexchange (SE) between the t(2g) core spins. We calculate the pressure dependence of T-C and compare it with the experimental phase diagram. Our results describe the experimental behaviour quite well only if a pressure-activated enhancement of the AF-SE interaction is assumed. RI Capone, Massimo/A-7762-200
Cristiani, ebrei e pagani: il dibattito sulla Sacra Scrittura tra III e VI secolo - Christians, Jews and Heathens: the Debate on the Holy Scripture between the Third and the Sixth Century
No full textMany of the contributions here collected were presented on the International Day of Studies entitled "Cristiani, ebrei e pagani: il dibattito sulla Sacra Scrittura tra III e VI secolo", held in Lecce (October 4th, 2013). The book explores the different approaches to the Sacred Scriptures by Christians, Jews and Heathens considered according to their various internal, geographical and chronological articulations, and more generally to the debate on the Scriptures developed between the 3rd and the 6th centuries in a society in which the interactions and meetings between peoples, religions and intellectuals were rather widespread. In particular, the contributions, which contribute to the reconstruction of a complex and articulated cultural landscape, are organized in three sections: I. Contraddizioni bibliche e cultura pagana (S. Morlet, C. Moreschini, A. Capone); II. Esegesi e polemica: Celso e Macario di Magnesia (E. Saponaro, P. De Giorgi, A. Cataldo); III. Ebrei, pagani e Sacre Scritture (P. Andrist, G. Rinaldi, M. Ryzhik)
Salerno. Un progetto di paesaggio
No full textEsperti di storia delle idee, di progettazione architettonica e del paesaggio, storici e storici dell’arte, botanici e curatori di orti botanici, filologi e studiosi di comunicazione visiva hanno collaborato al comune obiettivo di delineare un sistema integrato per la valorizzazione del paesaggio di Salerno, articolato tra i luoghi reali e simbolici tramandati dalla storia locale: la città, il Giardino della Minerva, il Castello di Arechi e l'Egerton 747, un codice botanico miniato di «argomento» salernitano.
La ricognizione di forme antiche della conoscenza, la riconversione fruitiva dei beni culturali e ambientali, l'approfondimento degli aspetti gestionali e divulgativi interpretano, attraverso il confronto delle esperienze e l'elaborazione di letture e di proposte progettuali applicate al caso salernitano, il rinnovamento dell'idea del giardino botanico e della sua tradizione, aprendola alle tematiche contemporanee della tutela dell'ambiente naturale, della costruzione del paesaggio e delle sue valenze culturali.
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Scritti di: Paola Capone, Vincenzo De Luca, Pierfranco Galliani, Franco Giorgetta, Luciano Mauro, Gennaro Miccio, Sue Minter, Antonio Piva, John F. Reed, Lucia Tongiorgi Tomasi, Guelfo Tozzi, Iolanda Ventura, Massimo Venturi Ferriolo, Alberto Vignolo
«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
Temperature dependence of the optical spectral weight in the cuprates: Role of electron correlations
No full textWe compare calculations based on the dynamical mean-field theory of the Hubbard model with the infrared spectral weight W(Omega,T) of La2-xSrxCuO4 and other cuprates. Without using fitting parameters we show that most of the anomalies found in W(Omega,T) with respect to normal metals, including the existence of two different energy scales for the doping and the T dependence of W(Omega,T), can be ascribed to strong correlation effects. RI Capone, Massimo/A-7762-200
Lectio magistralis: Bernard Lassus. Per una demarche globale? Il paesaggio
No full textIntervento di presentazine dell'opera di Bernard lassus, in occasione della Lectio Magistralis di B. Lassus e della pubblicazione del volume di P. Capone, "Il restauro impossibile. Un progetto di Bernard Lassus per il Cilento", 2012. Organizzato dalla Facoltà di Architettura di Roma in collaborazione con il Dipartimento di Scienze Politiche Sociali e della Comunicazione dell'Università di Salerno
Unraveling the polar state in TMTTF2-PF6 organic crystals
No full textCombining density-functional theory and many-body approaches we investigate the origin of the ferroelectric phase generally observed in TMTTF2-X organic crystals. We solve by means of mean-field theory and exact diagonalization a two-dimensional tight-biding model built from density-functional theory calculations and we show that short-range interactions stabilize a dimerized charge-ordered state in a wide range of parameters. Two different charge-ordering patterns are found; these correspond to those observed for X = PF6 and X = SCN. In the former case, a lattice dimerization couples with the charge ordering, leading to a polarization. Due to the interplay between charge and magnetic ordering, such polarization appears to be magnetically driven, thus revealing TMTTF2-PF6 as a multiferroic material. RI Capone, Massimo/A-7762-200
Dynamical mean field theory of polarons and bipolarons in the half-filled Holstein model
No full textThe evolution of the properties of a finite density electronic system as a function of the electron-phonon coupling is investigated in the Holstein model using the dynamical mean-field theory (DMFT) that becomes exact in infinite dimensions. We compare the spinless fermion case, in which only isolated polarons can be formed, with the spinful model in which the polarons can bind and form bipolarons. In the latter case, the bipolaronic binding occurs within DMFT as a metal-insulator transition. In the adiabatic regime in which the phonon energy is small with respect to the electron hopping we compare numerically exact DMFT results with an analytical scheme inspired by the Born-Oppenheimer procedure. Within the latter approach, a truncation of the phononic Hilbert space leads to a mapping of the original model onto an Anderson spin-fermion model. In the anti-adiabatic regime (where the phonon energy exceeds the electronic scales) the standard treatment based on Lang-Firsov canonical transformation allows one to map the original model on to an attractive Hubbard model in the spinful case. The separate analysis of the two regimes supports the numerical evidence that the presence of well-defined polaronic lattice displacements is not necessarily associated to a metal-insulator transition, which is instead due to pairing between the carriers. The finite-dimensionality effects neglected in DMFT may lead to a finite conductivity in the bipolaronic state which is, however, not always associated with polaronic distortions. At the polaron crossover the Born-Oppenheimer approximation is shown to break down due to the entanglement of the electron-phonon state. RI Capone, Massimo/A-7762-200
Isotope effects in the Hubbard-Holstein model within dynamical mean-field theory
No full textWe study the isotope effects arising from the coupling of correlated electrons with dispersionless phonons by considering the Hubbard-Holstein model at half-filling within the dynamical mean-field theory. In particular we calculate the isotope effects on the quasiparticle spectral weight Z, the renormalized phonon frequency, and the static charge and spin susceptibilities. In the weakly correlated regime U/t less than or similar to 1.5, where U is the Hubbard repulsion and t is the bare electron half-bandwidth, the physical properties are qualitatively similar to those characterizing the Holstein model in the absence of Coulomb repulsion, where the bipolaronic binding takes place at large electron-phonon coupling and it is reflected in divergent isotope responses. On the contrary in the strongly correlated regime U/t greater than or similar to 1.5, where the bipolaronic metal-insulator transition becomes of first order, the isotope effects are bounded, suggesting that the first-order transition is likely driven by an electronic mechanism, rather then by a lattice instability. These results point out how the isotope responses are extremely sensitive to phase boundaries and they may be used to characterize the competition between the electron-phonon coupling and the Hubbard repulsion. RI Capone, Massimo/A-7762-2008; Grimaldi, Claudio/B-1641-201
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