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Search Results: 1 - 10 of 3446 matches for " Federico Cilento "
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Optical control of non-equilibrium superconducting phase transition below Tc in a cuprate
Claudio Giannetti,Giacomo Coslovich,Federico Cilento,Gabriele Ferrini,Hiroshi Eisaki,Nobuhisa Kaneko,Martin Greven,Fulvio Parmigiani
Physics , 2008, DOI: 10.1103/PhysRevB.79.224502
Abstract: Photoinduced phase transitions from insulating to metallic states, accompanied by structural re-arrangements, have been recently reported in complex transition-metal oxides. However, the optical control of a purely electronic phase transition, where the thermodynamic phase is determined by the distribution of excitations, has remained elusive. Here we report optical control of the electronic phase in an underdoped Bi2212 crystal through impulsive photoinjection of quasiparticles (QP) via ultrashort laser pulses, avoiding significant laser heating. An abrupt transition of the transient optical electronic response is observed at a critical fluence of Ipump=70 uJ/cm^2. We show that the measured dynamics is consistent with an inhomogenous first-order superconducting-to-normal state phase transition, triggered by a sudden shift of the chemical potential.
Dumbarton Oaks. Byzantine Studies Dumbarton Oaks. Byzantine Studies
Adele Cilento
Reti Medievali Rivista , 2002, DOI: 10.6092/1593-2214/266
Abstract: Review of Dumbarton Oaks. Byzantine Studies Recensione a Dumbarton Oaks. Byzantine Studies
Ultrafast insulator-to-metal phase transition as a switch to measure the spectrogram of a supercontinuum light pulse
Federico Cilento,Claudio Giannetti,Gabriele Ferrini,Stefano Dal Conte,Tommaso Sala,Giacomo Coslovich,Matteo Rini,Andrea Cavalleri,Fulvio Parmigiani
Physics , 2009, DOI: 10.1063/1.3291105
Abstract: In this letter we demonstrate the possibility to determine the temporal and spectral structure (spectrogram) of a complex light pulse exploiting the ultrafast switching character of a non-thermal photo-induced phase transition. As a proof, we use a VO2 multi-film, undergoing an ultrafast insulator-to-metal phase transition when excited by femtosecond near-infrared laser pulses. The abrupt variation of the multi-film optical properties, over a broad infrared/visible frequency range, is exploited to determine, in-situ and in a simple way, the spectrogram of a supercontinuum pulse produced by a photonic crystal fiber. The determination of the structure of the pulse is mandatory to develop new pump-probe experiments with frequency resolution over a broad spectral range (700-1100 nm).
Dynamical coupling between off-plane phonons and in-plane electronic excitations in superconducting YBCO
Daniele Fausti,Fabio Novelli,Gianluca Giovannetti,Adolfo Avella,Federico Cilento,Luc Patthey,Milan Radovic,Massimo Capone,Fulvio Parmigiani
Physics , 2014,
Abstract: The interaction between phonons and high-energy excitations of electronic origin in cuprates and their role on the superconducting phenomenon is still controversial. Here, we use coherent vibrational time-domain spectroscopy together with density functional and dynamical mean-field theory calculations to establish a direct link between the c-axis phonon modes and the in-plane electronic charge excitations in optimally doped YBCO. Our findings clarify the nature of the anomalous high-energy response associated to the formation of the superconducting phase in the cuprates.
Hubbard exciton revealed by time-domain optical spectroscopy
Fabio Novelli,Daniele Fausti,Julia Reul,Federico Cilento,P. H. M. van Loosdrecht,A. A. Nugroho,T. T. M. Palstra,Markus Grüninger,Fulivo Parmigiani
Physics , 2012, DOI: 10.1103/PhysRevB.86.165135
Abstract: We use broadband ultra-fast pump-probe spectroscopy in the visible range to study the lowest excitations across the Mott-Hubbard gap in the orbitally ordered insulator YVO3. Separating thermal and non-thermal contributions to the optical transients, we show that the total spectral weight of the two lowest peaks is conserved, demonstrating that both excitations correspond to the same multiplet. The pump-induced transfer of spectral weight between the two peaks reveals that the low-energy one is a Hubbard exciton, i.e. a resonance or bound state between a doublon and a holon. Finally, we speculate that the pump-driven spin-disorder can be used to quantify the kinetic energy gain of the excitons in the ferromagnetic phase.
In search for the pairing glue in cuprates by non-equilibrium optical spectroscopy
Federico Cilento,Stefano Dal Conte,Giacomo Coslovich,Francesco Banfi,Gabriele Ferrini,Hiroshi Eisaki,Martin Greven,Andrea Damascelli,Dirk van der Marel,Fulvio Parmigiani,Claudio Giannetti
Physics , 2013, DOI: 10.1088/1742-6596/449/1/012003
Abstract: In strongly correlated materials the electronic and optical properties are significantly affected by the coupling of fermionic quasiparticles to different degrees of freedom, such as lattice vibrations and bosonic excitations of electronic origin. Broadband ultrafast spectroscopy is emerging as the premier technique to unravel the subtle interplay between quasiparticles and electronic or phononic collective excitations, by their different characteristic timescales and spectral responses. By investigating the femtosecond dynamics of the optical properties of Y-Bi2212 crystals over the 0.5-2 eV energy range, we disentangle the electronic and phononic contributions to the generalized electron-boson Eliashberg function, showing that the spectral distribution of the electronic excitations, such as spin fluctuations and current loops, and the strength of their interaction with quasiparticles can account for the high critical temperature of the superconducting phase transition. Finally, we discuss how the use of this technique can be extended to the underdoped region of the phase diagram of cuprates, in which a pseudogap in the quasiparticle density of states opens. The microscopic modeling of the interaction of ultrashort light pulses with unconventional superconductors will be one of the key challenges of the next-years materials science, eventually leading to the full understanding of the role of the electronic correlations in controlling the dynamics on the femtosecond timescale.
Pulsed homodyne Gaussian quantum tomography with low detection efficiency
Martina Esposito,Fabio Benatti,Roberto Floreanini,Stefano Olivares,Francesco Randi,Kelvin Titimbo,Marco Pividori,Fabio Novelli,Federico Cilento,Fulvio Parmigiani,Daniele Fausti
Physics , 2013, DOI: 10.1088/1367-2630/16/4/043004
Abstract: Pulsed homodyne quantum tomography usually requires a high detection efficiency limiting its applicability in quantum optics. Here, it is shown that the presence of low detection efficiency ($<50\%$) does not prevent the tomographic reconstruction of quantum states of light, specifically, of Gaussian type. This result is obtained by applying the so-called "minimax" adaptive reconstruction of the Wigner function to pulsed homodyne detection. In particular, we prove, by both numerical and real experiments, that an effective discrimination of different Gaussian quantum states can be achieved. Our finding paves the way to a more extensive use of quantum tomographic methods, even in physical situations in which high detection efficiency is unattainable.
Retos del hábitat urbano venezolano
Alfredo Cilento Sarli
Espacio Abierto , 2000,
Abstract: A partir de una visión comprehensiva de la situación de los asentamientos humanos venezolanos a finales del siglo XX, en este ensayo se plantean una serie de retos, como lineamientos de política que deberían tener vigencia durante un lapso no menor de diez a quince a os, dirigidos al logro de un hábitat urbano sostenible política, social, económica, técnica y ambientalmente.
Capacidad de resistencia, vulnerabilidad y cultura de riesgos
Alfredo Cilento Sarli
Espacio Abierto , 2005,
Abstract: La ocurrencia de cataclismos como sismos, aludes, tsunamis, huracanes, entre otros, constituyen amenazas naturales para los seres vivos, pero los seres humanos son los que convierten las amenazas en contingencias desastrosas. Por ello, la lucha contra los desastres provocados por los hombres y mujeres que habitan el planeta, es la batalla por el logro de una cultura de seguridad y prevención, respetuosa del medio ambiente natural y de la calidad del medio construido. Esa cultura deriva de la capacidad de resistencia de la población, y de una adecuada educación y preparación para enfrentar las contingencias antes de que ocurran, durante su ocurrencia y después de ocurridas. El fin determinante es el de salvar vidas y propiedades, y recuperar las facilidades para la vida y el trabajo, corrigiendo las fallas y vicios existentes antes de ocurrida la contingencia. En el desarrollo de esa cultura de seguridad el papel de las comunidades educativas, académicas y científicas es preponderante, al igual que la justa evaluación de la capacidad de resistencia de la sociedad, como elemento clave en los estudios de vulnerabilidad de los asentamientos humanos. En este trabajo se plantean algunos de los esfuerzos atribuibles a los actores mencionados, particularmente a las universidades públicas, dentro del marco de la Década de la Educación para el Desarrollo Sostenible 2005-2014, designada por Naciones Unidas.
Disentangling the electronic and phononic glue in a high-Tc superconductor
Stefano Dal Conte,Claudio Giannetti,Giacomo Coslovich,Federico Cilento,Davide Bossini,Tadesse Abebaw,Franceco Banfi,Gabriele Ferrini,Hiroshi Eisaki,Martin Greven,Andrea Damascelli,Dirk van der Marel,F. Parmigiani
Physics , 2012, DOI: 10.1126/science.1216765
Abstract: Unveiling the nature of the bosonic excitations that mediate the formation of Cooper pairs is a key issue for understanding unconventional superconductivity. A fundamen- tal step toward this goal would be to identify the relative weight of the electronic and phononic contributions to the overall frequency (\Omega) dependent bosonic function, \Pi(\Omega). We perform optical spectroscopy on Bi2212 crystals with simultaneous time- and frequency-resolution; this technique allows us to disentangle the electronic and phononic contributions by their different temporal evolution. The strength of the interaction ({\lambda}~1.1) with the electronic excitations and their spectral distribution fully account for the high critical temperature of the superconducting phase transition.
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