Beyond Mean-Field Corrections to the Quasiparticle Spectrum of Superfluid Fermi Gases

Loon, Senne Van; Tempere, J.; Kurkjian, Hadrien

doi:10.1103/physrevlett.124.073404

Cited by 8 publications

(14 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We keep track of the complex pole using the fitted energy z This is in stark contrast to previous results of Ref. [48] taking into account only the 1 → 2 disintegration, where the damping rate is sharply peaked when the eigenenergy reaches the threshold 1→3 th . This peaked behavior is washed out by including the now resonant 1 → 3 process in the self-energy, which sharply reduces the quasiparticle lifetime.…”

Section: Numerical Resultsmentioning

confidence: 98%

“…Near the dispersion minimum, this forbids a linearisation of Eq. ( 36) where Σ would be treated as an infinitesimal [48]. Although in general it is not possible to separate the contributions of the different disintegration processes, the appearance of the Hartree shift in the BCS limit can be understood to be mainly coming from Σ bc , as it is not present when only including the 1 → 2 process [48].…”

Section: Low-energy Propertiesmentioning

confidence: 99%

See 1 more Smart Citation

Quasiparticle disintegration in fermionic superfluids

Van Loon,

Tempere,

Kurkjian

2021

Preprint

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Numerical Resultsmentioning

confidence: 98%

Section: Low-energy Propertiesmentioning

confidence: 99%

Quasiparticle disintegration in fermionic superfluids

Van Loon,

Tempere,

Kurkjian

2021

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…In the framework of linear response theory, we seek the response of the system to first order in the fields φ and u σ . We thus neglect the quantum fluctuations in the terms of the equations of motion deriving from 38,51 : one writes the Heisenberg equations of motion for the bilinear fermionic operators (17) and linearizes them using incomplete Wick contractions (i.e. the replacement abcd ab cd ab cd ac bd ac bd…”

Section: Rpa Equations Of Motion In Presence Of Drive Fieldsmentioning

confidence: 99%

Linear response of a superfluid Fermi gas inside its pair-breaking continuum

Kurkjian

Tempere

Klimin

2020

Sci Rep

View full text Add to dashboard Cite

We study the signatures of the collective modes of a superfluid Fermi gas in its linear response functions for the order-parameter and density fluctuations in the Random Phase Approximation (RPA). We show that a resonance associated to the Popov-Andrianov (or sometimes "Higgs") mode is visible inside the pair-breaking continuum at all values of the wavevector q, not only in the (order-parameter) modulusmodulus response function but also in the modulus-density and density-density responses. At nonzero temperature, the resonance survives in the presence of thermally broken pairs even until the vicinity of the critical temperature T c , and coexists with both the Anderson-Bogoliubov modes at temperatures comparable to the gap Δ and with the low-velocity phononic mode predicted by RPA near T c. The existence of a Popov-Andrianov-"Higgs" resonance is thus a robust, generic feature of the high-energy phenomenology of pair-condensed Fermi gases, and should be accessible to state-of-the-art cold atom experiments. A primary way to probe the collective mode spectrum of a many-body system is by measuring the response functions of its macroscopic observables such as its density, or, in the case of a condensed system, its order parameter. These response functions can be measured by driving the system at a given wavenumber q and varying the drive frequency ω. In the theoretical case where the collective mode is undamped, one expects a infinitely narrow resonance (a Dirac peak) when ω coincides with the collective mode frequency ω q. However, in most systems, collective modes are coupled to one or several continua of excitations, for example by intrinsic couplings to other elementary excitations. The system response in this case is less abrupt: the response functions are nonzero at all frequencies ω belonging to the continuum and the Dirac peak of the collective mode is replaced, in the favorable cases, by a broadened resonance. Theoretically, this damped resonance can be related to the existence of a pole in the analytic continuation of the response functions through their branch cuts associated to the continua 1-3. Eventually, if the coupling to the continuum is very strong, the resonance may entirely disappear, such that only a slowly varying response remains visible inside the continuum. Superfluid Fermi gases, which one can form by cooling down fermionic atoms prepared in two internal states ↑ ↓ / 4-13 , offer a striking example of this fundamental many-body phenomenon. This system of condensed pairs of ↑ ↓ / fermions is described by 3 collective fields: the total density ρ of particles and the phase and modulus of the order-parameter Δ. In the general case, the fluctuations of those 3 fields are coupled and the collective modes have components on all of them. The system has also fermionic quasiparticles describing the breaking of pairs into unpaired fermions 14-17 , and two fermionic continua of quasiparticle biexcitations: a gapped quasiparticle-quasiparticle continuum and a gapless quasiparticle-quasihole continuum (to ...

show abstract

“…The rest of the derivation is similar to what is explained in Refs. [38,51]: one writes the Heisenberg equations of motion for the bilinear fermionic operators (17) and linearizes them using incomplete Wick contractions (i.e the replacement âb ĉ d…”

Section: Rpa Equations Of Motion In Presence Of Drive Fieldsmentioning

confidence: 99%

“…In the general case, the fluctuations of those 3 fields are coupled and the collective modes have components on all of them. The system has also fermionic quasiparticles describing the breaking of pairs into unpaired fermions [14][15][16][17], and two fermionic continua of quasiparticle biexcitations: a gapped quasiparticlequasiparticle continuum and a gapless quasiparticle-quasihole continuum (to which the collective modes are coupled only at nonzero temperature). Since the coupling to these continua is not small in general, the collective mode spectrum can be obtained only after nonperturbative analytic continuations [18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%