1,720,973 research outputs found
BCS-BEC crossover at finite temperature in the broken-symmetry phase
No full textThe BCS-BEC crossover is studied in a systematic way in the broken-symmetry phase between zero temperature
and the critical temperature. This study bridges two regimes where quantum and thermal fluctuations
are, respectively, important. The theory is implemented on physical grounds, by adopting a fermionic selfenergy
in the broken-symmetry phase that represents fermions coupled to superconducting fluctuations in weak
coupling and to bosons described by the Bogoliubov theory in strong coupling. This extension of the theory
beyond mean field proves important at finite temperature, to connect with the results in the normal phase. The
order parameter, the chemical potential, and the single-particle spectral function are calculated numerically for
a wide range of coupling and temperature. This enables us to assess the quantitative importance of superconducting
fluctuations in the broken-symmetry phase over the whole BCS-BEC crossover. Our results are relevant
to the possible realizations of this crossover with high-temperature cuprate superconductors and with ultracold fermionic atoms in a trap
Peaks and widths of radio-frequency spectra: An analysis of the phase diagram of ultra-cold Fermi gases
Full text linkWe provide a comprehensive theoretical study of the radio-frequency (rf) spectra of a two-component Fermi gas
with balanced populations in the normal region of the temperature-vs-coupling phase diagram. In particular, rf
spectra are analyzed in terms of two characteristic peaks, which can be either distinct or overlapping. On the
BEC side of the crossover, these two contributions are associated with a fermionic quasi-particle peak and a
bosonic-like contribution due to pairing. On the BCS side of the crossover, the two peaks are instead associated
with interactions between particles occurring, respectively, at high or low relative momenta. Through this
two-peak analysis, we show how and to what extent the correlation between the widths of the rf spectra and
the pair size, previously identified in the superfluid phase at low temperature, can be extended to the normal
phase, as well as how the temperature-vs-coupling phase diagram of the BCS-BEC crossover can be partitioned
in a number of distinct physical sectors. Several analytic results for the shape and widths of the rf spectra are
also derived in appropriate temperature and coupling limits
Critical behavior of the thermopower near the metal-insulator transition
Full text linkThe diffusive behavior of the number-heat correlation function for an interacting disordered electronic system ..
Beyond-mean-field description of a trapped unitary Fermi gas with mass and population imbalance
Full text linkA detailed description is given of the phase diagram for a two-component unitary Fermi gas with mass and population imbalance, for both homogeneous and trapped systems. This aims at providing quantitative benchmarks for the normal-to-superfluid phase transition of a mass-imbalanced Fermi gas in the temperature-polarization parameter space. A self-consistent t -matrix approach is adopted, which has already proven to accurately describe the thermodynamic properties of the mass- and population-balanced unitary Fermi gas. Our results provide a guideline for the ongoing experiments on heteronuclear Fermi mixtures
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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