BCS-BEC crossover at finite temperature in the broken-symmetry phase

Pieri, P.; Pisani, L.; Strinati, G. C.

doi:10.1103/physrevb.70.094508

Cited by 143 publications

(237 citation statements)

References 52 publications

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“…This agreement suggests that the choice of the fermionic self-energy made in Ref. 2 captures the essential physics of the problem, as soon as the fermionic degrees of freedom get progressively quenched while forming composite bosons.…”

supporting

confidence: 55%

Comparison between a diagrammatic theory for the BCS-BEC crossover and quantum Monte Carlo results

2005

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Predictions for the chemical potential and the excitation gap recently obtained by our diagrammatic theory for the BCS-BEC crossover in the superfluid phase are compared with novel Quantum Monte Carlo results at zero temperature now available in the literature. A remarkable agreement is found between the results obtained by the two approaches.PACS numbers: 03.75. Ss, 03.75.Hh, 05.30.Jp The recent experimental realization of the BCS-BEC crossover with ultracold trapped Fermi atoms 1 has given impetus to theoretical investigations of this crossover. In a recent paper 2 , the t-matrix self-energy approach (originally conceived for the normal phase 3 ) was extended to the superfluid phase, aiming at improving the description of the BCS-BEC crossover by including pairing fluctuations on top of the BCS mean-field approach considered in Refs. 4 and 5.In this theory, the effects of the collective BogoliubovAnderson mode is explicitly included in the fermionic self-energy, thus generalizing the theory due to Popov for a weakly-interacting (dilute) superfluid Fermi gas 6 . The theory is based on a judicious choice of the fermionic self-energy, such that it reproduces the fermionic meanfield BCS behavior plus pairing fluctuations in the weakcoupling limit as well as the Bogoliubov description for the composite bosons which form in the strong-coupling limit. In the intermediate-coupling region of interest about the unitarity limit, where no small parameter exists to control the many-body approximations, the theory is able to capture the essential physics of the problem, as the excellent agreement with a previously available QMC calculation 7 at the unitarity point (k F a F ) −1 = 0 has already shown 8 , and as more extensively demonstrated by the present comparison with more recent QMC data 9,10 spanning the whole crossover region. The theory of Ref. 2 is completely ab initio and it contains no adjustable parameter. Although the comparison with QMC data is here limited to the zero-temperature limit where they are available, the predictions of the theory of Ref.

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confidence: 55%

Comparison between a diagrammatic theory for the BCS-BEC crossover and quantum Monte Carlo results

2005

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“…This is the origin of the bendover or first-order phase transition evident in Fig. 2 [26] and other figures in this paper. It is well known how to overcome this problem, namely one has to include many-body renormalization effects due to the interaction U M [25,27].…”

Section: Bcs-bec Crossover In the Superfluid Phasementioning

confidence: 79%

Superfluid density and condensate fraction in the BCS-BEC crossover regime at finite temperatures

et al. 2007

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The superfluid density is a fundamental quantity describing the response to a rotation as well as in two-fluid collisional hydrodynamics. We present extensive calculations of the superfluid density ρ s in the BCS-BEC crossover regime of a uniform superfluid Fermi gas at finite temperatures.We include strong-coupling or fluctuation effects on these quantities within a Gaussian approximation. We also incorporate the same fluctuation effects into the BCS single-particle excitations described by the superfluid order parameter ∆ and Fermi chemical potential µ, using the Nozières and Schmitt-Rink (NSR) approximation. This treatment is shown to be necessary for consistent treatment of ρ s over the entire BCS-BEC crossover. We also calculate the condensate fraction N c as a function of the temperature, a quantity which is quite different from the superfluid density ρ s . We show that the mean-field expression for the condensate fraction N c is a good approximation even in the strong-coupling BEC regime. Our numerical results show how ρ s and N c depend on temperature, from the weak-coupling BCS region to the BEC region of tightly-bound Cooper pair molecules. In a companion paper by the authors (cond-mat/0609187), we derive an equivalent expression for ρ s from the thermodynamic potential, which exhibits the role of the pairing fluctuations in a more explicit manner.

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“…However, fluctuation corrections to the number equation may be important in the intermediate regime 41 .…”

Section: Bcs To Bec Evolution At T =mentioning

confidence: 99%

Nonzero orbital angular momentum superfluidity in ultracold Fermi gases

Iskin¹,

Melo

2006

Phys. Rev. A

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We analyze the evolution of superfluidity for nonzero orbital angular momentum channels from the Bardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein condensation (BEC) limit in three dimensions. First, we analyze the low energy scattering properties of finite range interactions for all possible angular momentum channels. Second, we discuss ground state (T = 0) superfluid properties including the order parameter, chemical potential, quasiparticle excitation spectrum, momentum distribution, atomic compressibility, ground state energy and low energy collective excitations. We show that a quantum phase transition occurs for nonzero angular momentum pairing, unlike the s-wave case where the BCS to BEC evolution is just a crossover. Third, we present a gaussian fluctuation theory near the critical temperature (T = Tc), and we analyze the number of bound, scattering and unbound fermions as well as the chemical potential. Finally, we derive the time-dependent Ginzburg-Landau functional near Tc, and compare the Ginzburg-Landau coherence length with the zero temperature average Cooper pair size.

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BCS-BEC crossover at finite temperature in the broken-symmetry phase

Cited by 143 publications

References 52 publications

Comparison between a diagrammatic theory for the BCS-BEC crossover and quantum Monte Carlo results

Comparison between a diagrammatic theory for the BCS-BEC crossover and quantum Monte Carlo results

Superfluid density and condensate fraction in the BCS-BEC crossover regime at finite temperatures

Nonzero orbital angular momentum superfluidity in ultracold Fermi gases

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