Marche au hasard d’une quasi-particule massive dans le gaz de phonons d’un superfluide à très basse température

Castin, Yvan

doi:10.5802/crphys.37

Cited by 3 publications

(5 citation statements)

References 37 publications

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“…and their intersection as a function of k. The lower edge of C 1→3 (red solid curve in Fig. 4) has a simple analytic expression [49]:…”

Section: Structure Of the Disintegration Continuamentioning

confidence: 99%

“…th is never fulfilled), such that the fermionic disintegration process 1 → 3 never acts as the sole damping channel [49]. In a neutral gas, sector C thus has little practical importance, but the situation would be reversed in a charged superfluid where the bosonic branch acquires a large gap corresponding to the plasma frequency [19].…”

Section: Perturbative and Self-consistent Solutionsmentioning

confidence: 99%

“…It is now established that beyond the mean-field approximation the ideal quasiparticle picture only works at low energies. Away from their dispersion minimum, the quasiparticles can disintegrate [47][48][49], resulting in a nonzero damping. The gapped energy spectrum of the fermionic excitations makes sure that the main decay mechanism at low energies is the disintegration by emission of a phonon [50,51] (a sound wave of the Fermi gas, no to be confused with a lattice phonon in solid-state physics).…”

mentioning

confidence: 99%

“…The gapped energy spectrum of the fermionic excitations makes sure that the main decay mechanism at low energies is the disintegration by emission of a phonon [50,51] (a sound wave of the Fermi gas, no to be confused with a lattice phonon in solid-state physics). This kind of interaction between fermionic quasiparticles and collective modes was considered in several studies, either from the point of view of collective modes [26,[50][51][52], or to study their effect on the quasiparticle properties [49,53,54]. Although the order parameter cannot be immediately related to the quasiparticle gap beyond BCS theory, we also note that there exists several calculations of this quantity [41,[55][56][57] beyond the mean-field BCS approximation.…”

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confidence: 99%

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Quasiparticle disintegration in fermionic superfluids

2022

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We study the fermionic quasiparticle spectrum in a zero-temperature superfluid Fermi gas, and in particular how it is modified by different disintegration processes. On top of the disintegration by emission of a collective boson (1\to21→2, subject of a previous study, PRL , 073404), we consider here disintegration events where three quasiparticles are emitted (1\to31→3). We show that both disintegration processes are described by a tt-matrix self-energy (as well as some highly off-resonant vacuum processes), and we characterize the associated disintegration continua. At strong coupling, we show that the quasiparticle spectrum is heavily distorted near the 1\to31→3 disintegration threshold. Near the dispersion minimum, where the quasiparticles remain well-defined, the main effect of the off-shell disintegration processes is to shift the location of the minimum by a value that corresponds to the Hartree shift in the BCS limit. With our approximation of the self-energy, the correction to the energy gap with respect to the mean-field result however remains small, in contrast with experimental measurements.

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“…and their intersection as a function of k. The lower edge of C 1→3 (red solid curve in Fig. 4) has a simple analytic expression [49]:…”

Section: Structure Of the Disintegration Continuamentioning

confidence: 99%

Section: Perturbative and Self-consistent Solutionsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Quasiparticle disintegration in fermionic superfluids

2022

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“…In this perturbative approximation, the damping rate Γ k is nonzero if the mean-field energy is inside one of the disintegration continua, such that at least one decay process is resonant. When the mean-field energy k th is never fulfilled), such that the fermionic disintegration process 1 → 3 never acts as the sole damping channel [49]. In a neutral gas, sector C thus has little practical importance, but the situation would be reversed in a charged superfluid where the bosonic branch acquires a large gap corresponding to the plasma frequency [19].…”

Section: B Perturbative and Self-consistent Solutionsmentioning

confidence: 99%

Quasiparticle disintegration in fermionic superfluids

Van Loon,

Tempere,

Kurkjian

2021

Preprint

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We study the fermionic quasiparticle spectrum in a zero-temperature superfluid Fermi gas, and in particular how it is modified by different disintegration processes. On top of the disintegration by emission of a collective boson (1 → 2, subject of a previous study, PRL 124, 073404), we consider here disintegration events where three quasiparticles are emitted (1 → 3). We show that both disintegration processes are described by a t-matrix self-energy (as well as some highly offresonant vacuum processes), and we characterize the associated disintegration continua. At strong coupling, we show that the quasiparticle spectrum is heavily distorted near the 1 → 3 disintegration threshold. Near the dispersion minimum, where the quasiparticles remain well-defined, the main effect of the off-shell disintegration processes is to shift the location of the minimum by a value that corresponds to the Hartree shift in the BCS limit. With our approximation of the self-energy, the correction to the energy gap with respect to the mean-field result however remains small, in contrast with experimental measurements.

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Universal van der Waals Force between Heavy Polarons in Superfluids

2022

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We investigate the long-range behavior of the induced Casimir interaction between two spinless heavy impurities, or polarons, in superfluid cold atomic gases. With the help of effective field theory (EFT) of a Galilean invariant superfluid, we show that the induced impurity-impurity potential at long distance universally shows a relativistic van der Waals-like attraction (∼ 1/r 7 ) resulting from the exchange of two superfluid phonons. We also clarify finite temperature effects from the same two-phonon exchange process. The temperature T introduces the additional length scale cs/T with the speed of sound cs. Leading corrections at finite temperature scale as T 6 /r for distances r cs/T smaller than the thermal length. For larger distances the potential shows a nonrelativistic van der Waals behavior (∼ T /r 6 ) instead of the relativistic one. Our EFT formulation applies not only to weakly coupled Bose or Fermi superfluids but also to that composed of strongly correlated unitary fermions with a weakly coupled impurity. The sound velocity controls the magnitude of the van der Waals potential, which we evaluate for the fermionic superfluid in the BCS-BEC crossover.

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Marche au hasard d’une quasi-particule massive dans le gaz de phonons d’un superfluide à très basse température

Abstract: Marche au hasard d'une quasi-particule massive dans le gaz de phonons d'un superfluide à très basse température

Cited by 3 publications

References 37 publications

Quasiparticle disintegration in fermionic superfluids

Quasiparticle disintegration in fermionic superfluids

Quasiparticle disintegration in fermionic superfluids

Universal van der Waals Force between Heavy Polarons in Superfluids

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