Superfluidity and collective modes in a uniform gas of Fermi atoms with a Feshbach resonance

Yoji Ohashi, A. Griffin

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3 Citations (Scopus)

Abstract

We investigate strong-coupling superfluidity in a uniform two-component gas of ultracold Fermi atoms attractively interacting via quasimolecular bosons associated with a Feshbach resonance. This interaction is tunable by the threshold energy [Formula Presented] of the Feshbach resonance, becoming large as [Formula Presented] is decreased (relative to [Formula Presented] where [Formula Presented] is the Fermi energy of one component). In recent work, we showed that the enhancement of this tunable pairing interaction naturally leads to the BCS-BEC (Bose-Einstein condensation) crossover, where the character of the superfluid phase transition changes from the BCS type to a BEC of composite bosons consisting of preformed Cooper-pairs and Feshbach-induced molecules. In this paper, we extend our previous work and study both the quasiparticles and the collective dynamics of the superfluid phase below the phase-transition temperature [Formula Presented] limiting ourselves to a uniform gas. We show how the superfluid order parameter changes from the Cooper-pair amplitude [Formula Presented] to the square root of the number of condensed molecules [Formula Presented] associated with the Feshbach resonance, as the threshold energy [Formula Presented] is lowered. In the intermediate coupling regime, the superfluidity is shown to be characterized by an order parameter consisting of a superposition of [Formula Presented] and [Formula Presented] We also discuss the Goldstone mode associated with superfluidity, and show how its character smoothly changes from the Anderson-Bogoliubov phonon in the BCS regime to the Bogoliubov phonon in the BEC regime in the BCS-BEC crossover. The velocity of this Goldstone phonon mode is shown to strongly depend on the value of [Formula Presented] We also show that this Goldstone mode appears as a resonance in the spectrum of the density-density correlation function, which is experimentally accessible.

Original languageEnglish
Number of pages1
JournalPhysical Review A - Atomic, Molecular, and Optical Physics
Volume67
Issue number6
DOIs
Publication statusPublished - 2003 Jan 1
Externally publishedYes

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superfluidity
gases
atoms
crossovers
bosons
thresholds
energy
molecules
condensation
transition temperature
interactions

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

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title = "Superfluidity and collective modes in a uniform gas of Fermi atoms with a Feshbach resonance",
abstract = "We investigate strong-coupling superfluidity in a uniform two-component gas of ultracold Fermi atoms attractively interacting via quasimolecular bosons associated with a Feshbach resonance. This interaction is tunable by the threshold energy [Formula Presented] of the Feshbach resonance, becoming large as [Formula Presented] is decreased (relative to [Formula Presented] where [Formula Presented] is the Fermi energy of one component). In recent work, we showed that the enhancement of this tunable pairing interaction naturally leads to the BCS-BEC (Bose-Einstein condensation) crossover, where the character of the superfluid phase transition changes from the BCS type to a BEC of composite bosons consisting of preformed Cooper-pairs and Feshbach-induced molecules. In this paper, we extend our previous work and study both the quasiparticles and the collective dynamics of the superfluid phase below the phase-transition temperature [Formula Presented] limiting ourselves to a uniform gas. We show how the superfluid order parameter changes from the Cooper-pair amplitude [Formula Presented] to the square root of the number of condensed molecules [Formula Presented] associated with the Feshbach resonance, as the threshold energy [Formula Presented] is lowered. In the intermediate coupling regime, the superfluidity is shown to be characterized by an order parameter consisting of a superposition of [Formula Presented] and [Formula Presented] We also discuss the Goldstone mode associated with superfluidity, and show how its character smoothly changes from the Anderson-Bogoliubov phonon in the BCS regime to the Bogoliubov phonon in the BEC regime in the BCS-BEC crossover. The velocity of this Goldstone phonon mode is shown to strongly depend on the value of [Formula Presented] We also show that this Goldstone mode appears as a resonance in the spectrum of the density-density correlation function, which is experimentally accessible.",
author = "Yoji Ohashi and A. Griffin",
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AU - Ohashi, Yoji

AU - Griffin, A.

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N2 - We investigate strong-coupling superfluidity in a uniform two-component gas of ultracold Fermi atoms attractively interacting via quasimolecular bosons associated with a Feshbach resonance. This interaction is tunable by the threshold energy [Formula Presented] of the Feshbach resonance, becoming large as [Formula Presented] is decreased (relative to [Formula Presented] where [Formula Presented] is the Fermi energy of one component). In recent work, we showed that the enhancement of this tunable pairing interaction naturally leads to the BCS-BEC (Bose-Einstein condensation) crossover, where the character of the superfluid phase transition changes from the BCS type to a BEC of composite bosons consisting of preformed Cooper-pairs and Feshbach-induced molecules. In this paper, we extend our previous work and study both the quasiparticles and the collective dynamics of the superfluid phase below the phase-transition temperature [Formula Presented] limiting ourselves to a uniform gas. We show how the superfluid order parameter changes from the Cooper-pair amplitude [Formula Presented] to the square root of the number of condensed molecules [Formula Presented] associated with the Feshbach resonance, as the threshold energy [Formula Presented] is lowered. In the intermediate coupling regime, the superfluidity is shown to be characterized by an order parameter consisting of a superposition of [Formula Presented] and [Formula Presented] We also discuss the Goldstone mode associated with superfluidity, and show how its character smoothly changes from the Anderson-Bogoliubov phonon in the BCS regime to the Bogoliubov phonon in the BEC regime in the BCS-BEC crossover. The velocity of this Goldstone phonon mode is shown to strongly depend on the value of [Formula Presented] We also show that this Goldstone mode appears as a resonance in the spectrum of the density-density correlation function, which is experimentally accessible.

AB - We investigate strong-coupling superfluidity in a uniform two-component gas of ultracold Fermi atoms attractively interacting via quasimolecular bosons associated with a Feshbach resonance. This interaction is tunable by the threshold energy [Formula Presented] of the Feshbach resonance, becoming large as [Formula Presented] is decreased (relative to [Formula Presented] where [Formula Presented] is the Fermi energy of one component). In recent work, we showed that the enhancement of this tunable pairing interaction naturally leads to the BCS-BEC (Bose-Einstein condensation) crossover, where the character of the superfluid phase transition changes from the BCS type to a BEC of composite bosons consisting of preformed Cooper-pairs and Feshbach-induced molecules. In this paper, we extend our previous work and study both the quasiparticles and the collective dynamics of the superfluid phase below the phase-transition temperature [Formula Presented] limiting ourselves to a uniform gas. We show how the superfluid order parameter changes from the Cooper-pair amplitude [Formula Presented] to the square root of the number of condensed molecules [Formula Presented] associated with the Feshbach resonance, as the threshold energy [Formula Presented] is lowered. In the intermediate coupling regime, the superfluidity is shown to be characterized by an order parameter consisting of a superposition of [Formula Presented] and [Formula Presented] We also discuss the Goldstone mode associated with superfluidity, and show how its character smoothly changes from the Anderson-Bogoliubov phonon in the BCS regime to the Bogoliubov phonon in the BEC regime in the BCS-BEC crossover. The velocity of this Goldstone phonon mode is shown to strongly depend on the value of [Formula Presented] We also show that this Goldstone mode appears as a resonance in the spectrum of the density-density correlation function, which is experimentally accessible.

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