13 results on '"Perali, Andrea"'
Search Results
2. Evidence from quantum Monte Carlo of large gap superfluidity and BCS-BEC crossover in double electron-hole layers
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Ríos, Pablo López, Perali, Andrea, Needs, Richard J., and Neilson, David
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Condensed Matter::Quantum Gases ,Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter::Other ,Condensed Matter - Superconductivity ,FOS: Physical sciences - Abstract
We report quantum Monte Carlo evidence of the existence of large gap superfluidity in electron-hole double layers over wide density ranges. The superfluid parameters evolve from normal state to BEC with decreasing density, with the BCS state restricted to a tiny range of densities due to the strong screening of Coulomb interactions, which causes the gap to rapidly become large near the onset of superfluidity. The superfluid properties exhibit similarities to ultracold fermions and iron-based superconductors, suggesting an underlying universal behavior of BCS-BEC crossovers in pairing systems., Comment: 6 pages, 4 figures, 4 pages Supplementary. Submitted to Physical Review Letters
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- 2017
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3. Pairing-gap, pseudo-gap, and no-gap phases in the radio-frequency spectra of a trapped unitary 6Li gas
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Pieri, Pierbiagio, Perali, Andrea, STRINATI CALVANESE, Giancarlo, Riedl, S., Wright, M. J., Altmeyer, A., Kohstall, C., Sanchez Guajardo, E. R., Hecker Denschlag, J., Grimm, R., PIERI, Pierbiagio, PERALI, Andrea, STRINATI CALVANESE, Giancarlo, S. Riedl, M. J. Wright, A. Altmeyer, C. Kohstall, E. R. Sanchez Guajardo, J. Hecker Denschlag, and R. Grimm
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Condensed Matter::Quantum Gases ,Radio-frequency spectroscopy, ultracold Fermi gases ,Quantum Gases (cond-mat.quant-gas) ,FOS: Physical sciences ,Condensed Matter - Quantum Gases - Abstract
Radio frequency spectra of a trapped unitary 6Li gas are reported and analyzed in terms of a theoretical approach that includes both final-state and trap effects. Final-state effects play a crucial role in evidencing two main peaks both above and below the critical temperature Tc as being associated with two distinct phases that reside in different trap regions. These are the pairing-gap and pseudo-gap phases below Tc, which evolve into the pseudo-gap and no-gap phases above Tc. In this way, a long standing puzzle about the interpretation of rf spectra for 6Li in a trap is solved., Comment: 5 pages, 6 figures (final version)
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- 2011
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4. Hidden Pseudogap and Excitation Spectra in a Strongly Coupled Two-Band Superfluid/Superconductor
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Pierbiagio Pieri, Hiroyuki Tajima, Andrea Perali, Tajima, Hiroyuki, Pieri, Pierbiagio, and Perali, Andrea
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BCS-BEC crossover ,Crossover ,FOS: Physical sciences ,multiband superconductor ,BCS-BEC crossover, quantum gases, superconductivity, multi-band systems ,spectral function ,01 natural sciences ,010305 fluids & plasmas ,law.invention ,Superconductivity (cond-mat.supr-con) ,Superfluidity ,pseudogap ,multicomponent superfluids ,law ,Condensed Matter::Superconductivity ,0103 physical sciences ,010306 general physics ,Physics ,Superconductivity ,Condensed Matter::Quantum Gases ,Condensed matter physics ,Condensed Matter::Other ,Condensed Matter - Superconductivity ,Condensed Matter Physics ,lcsh:QC1-999 ,Electronic, Optical and Magnetic Materials ,Quantum Gases (cond-mat.quant-gas) ,Pairing ,Density of states ,Scanning tunneling microscope ,Condensed Matter - Quantum Gases ,Pseudogap ,lcsh:Physics ,Excitation - Abstract
We investigate single-particle excitation properties in the normal state of a two-band superconductor or superfluid throughout the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein-condensation (BEC) crossover, within the many-body T-matrix approximation for multi-channel pairing fluctuations. We address the single-particle density of states and the spectral functions consisting of two contributions associated with a waekly interacting deep band and a strongly interacting shallow band, relevant for iron-based multiband superconductors and multicomponent fermionic superfluids. We show how the pseudogap state in the shallow band is hidden by the deep band contribution throughout the two-band BCS-BEC crossover. Our results could explain the missing pseudogap in recent scanning tunneling microscopy experiments in FeSe superconductors., 13 pages, 3 figures, submitted to the Special Issue "Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors III" of Condensed Matter
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- 2021
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5. Observation of pseudogap behaviour in a strongly interacting Fermi gas
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Andrea Perali, Tara E. Drake, G. C. Strinati, John Gaebler, J. T. Stewart, Deborah Jin, Pierbiagio Pieri, J. P. Gaebler, J. T. Stewart, T. E. Drake, D. S. Jin, PERALI, Andrea, PIERI, Pierbiagio, and STRINATI CALVANESE, Giancarlo
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Condensed Matter::Quantum Gases ,Physics ,Condensed matter physics ,Condensed Matter::Other ,Condensed Matter - Superconductivity ,High Energy Physics::Lattice ,Optical physics ,FOS: Physical sciences ,General Physics and Astronomy ,Fermion ,Superconductivity (cond-mat.supr-con) ,Pseudogap, ultracold Fermi gases, BCS-BEC crossover ,Superfluidity ,Phase coherence ,Quantum Gases (cond-mat.quant-gas) ,Condensed Matter::Superconductivity ,Quantum mechanics ,Phase (matter) ,Condensed Matter::Strongly Correlated Electrons ,Condensed Matter - Quantum Gases ,Fermi gas ,Pseudogap - Abstract
Ultracold atomic Fermi gases present an opportunity to study strongly interacting fermionic systems in a controlled and uncomplicated setting. The ability to tune attractive interactions has led to the discovery of superfluidity in these systems with an extremely high transition temperature with respect to the Fermi temperature near T/TF=0.2. This superfluidity is the electrically neutral analogue of superconductivity; however, superfluidity in atomic Fermi gases occurs in the limit ofstrong interactions and defies a conventional Bardeen–Cooper– Schrieffer (BCS) description. For these strong interactions, it is predicted that the onset of pairing and superfluidity can occur at different temperatures. Thus, for a range of temperatures, a pseudogap region may exist, in which the system retains some of the characteristics of the superfluid phase—such as a BCS-like dispersion and a partially gapped density of states—but does not exhibit superfluidity. By making two independent measurements—the direct observation of pair condensation in momentum space and a measurement of the single-particle spectral function using an analogue to photoemission spectroscopy6—we directly probe the pseudogap phase. Our measurements reveal a BCS-like dispersion with back-bending near the Fermiwavevector kF, which persists well above the transition temperature for pair condensation.
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- 2010
6. Pairing effects in the normal phase of a two-dimensional Fermi gas
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Andrea Perali, Frank Marsiglio, Pierbiagio Pieri, F. Palestini, G. C. Strinati, F. Marsiglio, PIERI, Pierbiagio, PERALI, Andrea, PALESTINI, FABRIZIO, and STRINATI CALVANESE, Giancarlo
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Physics ,Condensed Matter::Quantum Gases ,Condensed matter physics ,Condensed Matter - Superconductivity ,Ultracold Fermi gases, superconductivity, pseudogap, low-dimensional systems ,Normal phase ,Crossover ,Boundary (topology) ,FOS: Physical sciences ,State (functional analysis) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Superfluidity ,Superconductivity (cond-mat.supr-con) ,Quantum Gases (cond-mat.quant-gas) ,Condensed Matter::Superconductivity ,Quantum mechanics ,Pairing ,Condensed Matter - Quantum Gases ,Pseudogap ,Fermi gas - Abstract
In a recent experiment [M. Feld et al., Nature 480, 75 (2011); B. Froehlich et al., Phys. Rev. Lett. 109,130403 (2012)], a pairing gap was detected in a two-dimensional (2D) Fermi gas with attractive interaction at temperatures where superfluidity does not occur. The question remains open as to whether this gap is a pseudogap phenomenon or is due to a molecular state. In this paper, by using a t-matrix approach, we reproduce quite well the experimental data for a 2D Fermi gas, and set the boundary between the pseudogap and molecular regimes. We also show that pseudogap phenomena occurring in 2D and 3D can be related through a variable spanning the BCS-BEC crossover in a universal way., Comment: 10 pages, 9 figures; final version
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- 2014
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7. Dispersions, weights, and widths of the single-particle spectral function in the normal phase of a Fermi gas
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F. Palestini, Pierbiagio Pieri, G. C. Strinati, Andrea Perali, PALESTINI, FABRIZIO, PERALI, Andrea, PIERI, Pierbiagio, and STRINATI CALVANESE, Giancarlo
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Condensed Matter::Quantum Gases ,Physics ,Range (particle radiation) ,Condensed matter physics ,Avoided crossing ,FOS: Physical sciences ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Quantum Gases (cond-mat.quant-gas) ,Spin wave ,Wave vector ,Fermi liquid theory ,Condensed Matter - Quantum Gases ,Pseudogap ,Fermi gas ,BCS-BEC crossover, ultracold Fermi gases ,Fermi Gamma-ray Space Telescope - Abstract
The dispersions, weights, and widths of the peaks of the single-particle spectral function in the presence of pair correlations, for a Fermi gas with either attractive or repulsive short-range inter-particle interaction, are determined in the normal phase over a wide range of wave vectors, with a twofold purpose. The first one is to determine how these dispersions identify both an energy scale known as the pseudo-gap near the Fermi wave vector, as well as an additional energy scale related to the contact C at large wave vectors. The second one is to differentiate the behaviors of the repulsive gas from the attractive one in terms of crossing versus avoided crossing of the dispersions near the Fermi wave vector. An analogy will also be drawn between the occurrence of the pseudo-gap physics in a Fermi gas subject to pair fluctuations and the persistence of local spin waves in the normal phase of magnetic materials., Comment: 18 pages, 21 figures
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- 2012
8. Evolution of the Normal State of a Strongly Interacting Fermi Gas from a Pseudogap Phase to a Molecular Bose Gas
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F. Palestini, Pierbiagio Pieri, John Gaebler, Deborah Jin, J. T. Stewart, Andrea Perali, G. C. Strinati, Tara E. Drake, PERALI, Andrea, PALESTINI, FABRIZIO, PIERI, Pierbiagio, STRINATI CALVANESE, Giancarlo, J. T. Stewart, J. P. Gaebler, T. E. Drake, and D. S. Jin
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Physics ,Condensed Matter::Quantum Gases ,Gas in a box ,Condensed matter physics ,Condensed Matter - Superconductivity ,Astrophysics::High Energy Astrophysical Phenomena ,Fermi level ,General Physics and Astronomy ,Quantum oscillations ,FOS: Physical sciences ,Fermi surface ,Fermi energy ,radio frequency spectroscopy, ultracold Fermi gases, pseudogap ,Superconductivity (cond-mat.supr-con) ,symbols.namesake ,Quantum Gases (cond-mat.quant-gas) ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Fermi liquid theory ,Fermi gas ,Pseudogap ,Condensed Matter - Quantum Gases - Abstract
Wave-vector resolved radio frequency (rf) spectroscopy data for an ultracold trapped Fermi gas are reported for several couplings at Tc, and extensively analyzed in terms of a pairing-fluctuation theory. We map the evolution of a strongly interacting Fermi gas from the pseudogap phase into a fully gapped molecular Bose gas as a function of the interaction strength, which is marked by a rapid disappearance of a remnant Fermi surface in the single-particle dispersion. We also show that our theory of a pseudogap phase is consistent with a recent experimental observation as well as with Quantum Monte Carlo data of thermodynamic quantities of a unitary Fermi gas above Tc., 9 pages, 9 figures. Substantially revised version (to appear in Phys. Rev. Lett.)
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- 2011
9. Temperature and coupling dependence of the universal contact intensity for an ultracold Fermi gas
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F. Palestini, G. C. Strinati, Pierbiagio Pieri, Andrea Perali, PALESTINI, FABRIZIO, PERALI, Andrea, PIERI, Pierbiagio, and STRINATI CALVANESE, Giancarlo
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Condensed Matter::Quantum Gases ,Physics ,Condensed matter physics ,Transition temperature ,FOS: Physical sciences ,Coupling (probability) ,Atomic and Molecular Physics, and Optics ,Superfluidity ,Many-body problem ,Quantum Gases (cond-mat.quant-gas) ,Pairing ,Condensed Matter - Quantum Gases ,Response functions, BCS-BEC crossover, ultracold gases, superconductivity ,Fermi gas ,Pseudogap ,Phase diagram - Abstract
Physical properties of an ultracold Fermi gas in the temperature-coupling phase diagram can be characterized by the contact intensity C, which enters the pair-correlation function at short distances and describes how the two-body problem merges into its surrounding. We show that the local order established by pairing fluctuations about the critical temperature Tc of the superfluid transition considerably enhances the contact C in a temperature range where pseudogap phenomena are maximal. Our ab initio results for C in a trap compare well with recently available experimental data over a wide coupling range. An analysis is also provided for the effects of trap averaging on C., Comment: 5 pages, 5 figures
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- 2010
10. Enhanced paraconductivity-like fluctuations in the radio frequency spectra of ultracold Fermi atoms
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Andrea Perali, G. C. Strinati, Pierbiagio Pieri, PIERI, Pierbiagio, PERALI, Andrea, and STRINATI CALVANESE, Giancarlo
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Superconductivity ,Physics ,Condensed Matter::Quantum Gases ,Condensed matter physics ,Condensed Matter - Superconductivity ,Strong interaction ,Optical physics ,General Physics and Astronomy ,FOS: Physical sciences ,Context (language use) ,Fermion ,Condensed Matter - Other Condensed Matter ,Superconductivity (cond-mat.supr-con) ,Pairing ,Condensed Matter::Superconductivity ,BCS-BEC crossover, superfluids, fluctuations ,Pseudogap ,Fermi Gamma-ray Space Telescope ,Other Condensed Matter (cond-mat.other) - Abstract
Ultracold Fermi atoms allow the realization of the crossover from Bardeen-Cooper-Schrieffer (BCS) superconductivity to Bose- Einstein condensation (BEC), by varying with continuity the attraction between fermions of different species. In this context, radio frequency (RF) spectroscopy provides a microscopic probe to infer the nature of fermionic pairing. In the strongly-interacting regime, this pairing affects a wide temperature range comprising the critical temperature T_c, in analogy to the pseudogap physics for high-temperature superconductors. By including what are known in superconductors as "paraconductivity" fluctuations, here we calculate the RF spectra above T_c for fermions with balanced populations and compare them with available experimental data, thus revealing that the role of these fluctuations is considerably enhanced with respect to superconductors. In addition, we extract from the spectra an energy scale associated with pairing and relate it to a universal quantity recently introduced for Fermi gases., Comment: 17 pages, 5 figures
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- 2008
- Full Text
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11. Extracting the condensate density from projection experiments with Fermi gases
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G. C. Strinati, Pierbiagio Pieri, Andrea Perali, PERALI, Andrea, PIERI, Pierbiagio, and STRINATI CALVANESE, Giancarlo
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Physics ,Condensed Matter::Quantum Gases ,Condensed matter physics ,Condensed Matter::Other ,Condensed Matter - Superconductivity ,Crossover ,FOS: Physical sciences ,General Physics and Astronomy ,BCS theory ,Ultracold Fermi gases, superfluidity, BCS-BEC crossover, many-body systems ,law.invention ,Superconductivity (cond-mat.supr-con) ,Many-body problem ,Superfluidity ,Condensed Matter - Other Condensed Matter ,Mean field theory ,law ,Pairing ,Condensed Matter::Superconductivity ,Fermi gas ,Bose–Einstein condensate ,Other Condensed Matter (cond-mat.other) - Abstract
A debated issue in the physics of the BCS-BEC crossover with trapped Fermi atoms is to identify characteristic properties of the superfluid phase. Recently, a condensate fraction was measured on the BCS side of the crossover by sweeping the system in a fast (nonadiabatic) way from the BCS to the BEC sides, thus ``projecting'' the initial many-body state onto a molecular condensate. We analyze here the theoretical implications of these projection experiments, by identifying the appropriate quantum-mechanical operator associated with the measured quantities and relating them to the many-body correlations occurring in the BCS-BEC crossover. Calculations are presented over wide temperature and coupling ranges, by including pairing fluctuations on top of mean field., 4 pages, 4 figures
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- 2005
12. Shrinking of a condensed fermionic cloud in a trap approaching the Bose-Einstein condensation limit
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Andrea Perali, Pierbiagio Pieri, G. C. Strinati, PERALI, Andrea, PIERI, Pierbiagio, and STRINATI CALVANESE, Giancarlo
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Condensed Matter::Quantum Gases ,Physics ,Condensed matter physics ,Fermion ,Atomic and Molecular Physics, and Optics ,law.invention ,Superfluidity ,Trap (computing) ,law ,Atomic theory ,Ultracold Fermi gases, BCS-BEC croossover ,Cooper pair ,Thomas–Fermi model ,Bose–Einstein condensate ,Order of magnitude - Abstract
We determine the zero-temperature density profile of a cloud of fermionic atoms in a trap subject to a mutual attractive interaction, as the strength of the interaction is progressively increased. We find a significant decrease of the size of the atomic cloud as it evolves from the weak-coupling regime of overlapping Cooper pairs to the strong-coupling ~Bose-Einstein! regime of nonoverlapping bound-fermion pairs. Most significantly, we find a pronounced increase of the value of the density at the center of the trap ~even by an order of magnitude! when evolving between the two regimes. Our results are based on a generalized Thomas-Fermi approximation for the superfluid state, which covers continuously all coupling regimes.
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- 2003
13. Density-induced BCS to Bose-Einstein crossover
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N. Andrenacci, G. C. Strinati, Andrea Perali, Pierbiagio Pieri, ANDRENACCI N., PERALI, Andrea, PIERI, Pierbiagio, and STRINATI CALVANESE, Giancarlo
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Condensed Matter::Quantum Gases ,Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Hubbard model ,Condensed matter physics ,Condensed Matter - Superconductivity ,Crossover ,FOS: Physical sciences ,Fermion ,Superconductors, BCS-BEC crossover ,Square lattice ,law.invention ,Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,law ,Quantum mechanics ,Antiferromagnetism ,Particle density ,Bose–Einstein condensate ,Boson - Abstract
We investigate the zero-temperature BCS to Bose-Einstein crossover at the mean-field level, by driving it with the attractive potential and the particle density.We emphasize specifically the role played by the particle density in this crossover.Three different interparticle potentials are considered for the continuum model in three spatial dimensions, while both s- and d-wave solutions are analyzed for the attractive (extended) Hubbard model on a two-dimensional square lattice. For this model the peculiar behavior of the crossover for the d-wave solution is discussed.In particular, in the strong-coupling limit when approaching half filling we evidence the occurrence of strong correlations among antiparallel-spin fermions belonging to different composite bosons, which give rise to a quasi-long-range antiferromagnetic order in this limit., 10 pages, 5 enclosed figures
- Published
- 1999
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