Leggett collective excitations in a two-band Fermi superfluid at finite temperatures

Klimin, S. N.; Kurkjian, Hadrien; Tempere, J.

doi:10.1088/1367-2630/ab54b0

Cited by 13 publications

(12 citation statements)

References 29 publications

(121 reference statements)

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“…The superfluid properties in a multi-band (or multi-component) system have been attracting a great interests 1 – 4 . In comparing with single-band superfluid counterpart, a lot of novel physics, for example, existence of gapped Leggett modes 5 – 9 , color superconductor 10 – 12 , coexistence of superfluid and ferromagnetic polarizations 13 , 14 , induced effective interaction 15 , breaking of Galilean invariance in spin-orbit coupled Bose–Einstein condensation (BEC) 16 , etc, would appear.…”

Section: Introductionmentioning

confidence: 99%

Superfluid density and collective modes of fermion superfluid in dice lattice

Zhang

Liu

et al. 2021

Sci Rep

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The superfluid properties of attractive Hubbard model in dice lattice are investigated. It is found that three superfluid order parameters increase as the interaction increases. When the filling factor falls into the flat band, due to the infinite large density of states, the resultant superfluid order parameters are proportional to interaction strength, which is in striking contrast with the exponentially small counterparts in usual superfluid (or superconductor). When the interaction is weak, and the filling factor is near the bottom of the lowest band (or the top of highest band), the superfluid density is determined by the effective mass of the lowest (or highest) single-particle band. When the interaction is strong and filling factor is small, the superfluid density is inversely proportional to interaction strength, which is related to effective mass of tightly bound pairs. In the strong interaction limit and finite filling, the asymptotic behaviors of superfluid density can be captured by a parabolic function of filling factor. Furthermore, when the filling is in flat band, the superfluid density shows a logarithmic singularity as the interaction approaches zero. In addition, there exist three undamped collective modes for strong interactions. The lowest excitation is gapless phonon, which is characterized by the total density oscillations. The two others are gapped Leggett modes, which correspond relative density fluctuations between sublattices. The collective modes are also reflected in the two-particle spectral functions by sharp peaks. Furthermore, it is found that the two-particle spectral functions satisfy an exact sum-rule, which is directly related to the filling factor (or density of particle). The sum-rule of the spectral functions may be useful to distinguish between the hole-doped and particle-doped superfluid (superconductor) in experiments.

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Section: Introductionmentioning

confidence: 99%

Superfluid density and collective modes of fermion superfluid in dice lattice

Zhang

Liu

et al. 2021

Sci Rep

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“…The possibility of the Leggett mode has been examined in Refs. [7,14]; however, Ref. [3] predicted that it is severely damped in a 173 Yb Fermi gas.…”

Section: Introductionmentioning

confidence: 99%

“…Since the proposal of a Feshbach resonance using the orbital degrees of freedom in 2015 [1], this so-called orbital Feshbach resonance (OFR) has attracted much attention as a candidate for the pairing mechanism of a 173 Yb Fermi gas [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Although the superfluid phase transition of this alkaline-earth-like Fermi gas has not been realized yet, experimental groups have succeeded in tuning the strength of a pairing interaction between 173 Yb atoms, by adjusting the threshold energy of OFR [17,18].…”

Section: Introductionmentioning

confidence: 99%

Superfluid properties of an ultracold Fermi gas with an orbital Feshbach resonance in the BCS-BEC crossover region

Kamihori,

Kagamihara,

Ohashi

2021

Preprint

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We theoretically investigate superfluid properties of a two-band gas of 173 Yb Fermi atoms with an orbital Feshbach resonance (OFR). To describe the BCS-BEC crossover region, we include superfluid fluctuations caused by inter-band and intra-band pairing interactions associated with OFR, by extending the strong-coupling theory developed by Nozières and Schmitt-Rink to the twoband case below the superfluid phase transition temperature; however, effects of an experimentally inaccessible deep bound state are removed, to model a real 173 Yb Fermi gas near OFR. We show that the condensate fraction in the upper closed channel gradually becomes smaller than that in the lower open channel, as one moves from the strong-to the weak-coupling regime, because the OFR-pairing mechanism tunes the interaction strengths by adjusting the energy difference between the two bands. However, even when the closed-channel band is much higher in energy than the open-channel band in the weak-coupling regime, the magnitude of the superfluid order parameter in the closed channel is found to be still comparable to that in the open channel. As the reason for this, we point out a pair-tunneling effect by the OFR-induced inter-band interaction. Besides these superfluid quantities, we also examine collective modes, such as the Goldstone mode, Schmid (Higgs) mode, as well as Leggett mode, to clarify how they appear in the spectral weights of paircorrelation functions in each band. Since the realization of a multi-band superfluid Fermi gas is a crucial issue in cold Fermi gas physics, our results would contribute to the basic understanding of this type of Fermi superfluid in the BCS-BEC crossover region.

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“…The superfluid properties in multi-component (or multi-band) system have been attracting a great interests [1][2][3] . In comparing with single-component superfluid counterpart, a lot of novel physics, for example, existence of gapped Leggett modes [4][5][6][7][8] , color superconductor [9][10][11] , coexistence of superfluid and ferromagnetic polarizations 12,13 , induced effective interaction 14 , breaking of Galilean invariance in spin-orbit coupled Bose-Einstein condensation (BEC) 15 , etc, in multi-component superfluid would appear.…”

Section: Introductionmentioning

confidence: 99%

Superfluid Density and Collective Modes of Fermion Superfluid in Dice Lattice

Zhang

Liu

et al. 2021

Preprint

View full text Add to dashboard Cite

The superfluid properties of attractive Hubbard model in dice lattice are investigated. It is found that three superfluid order parameters increase as the interaction increases. When the filling factor falls into the flat band, due to the infinite large density of states, the resulting superfluid order parameters are proportional to interaction strength, which is in striking contrast with the exponentially small counterparts in usual superfluid (or superconductor). When the interaction is weak and the filling factor is near the bottom of lowest band (or the top of highest band), the superfluid density is determined by the effective mass of the lowest (or highest) single-particle band. When the interactions is strong and filling factor is small, the superfluid density is inversely proportional to interaction strength, which is related to effective mass of tightly bound pairs. In the strong interaction limit and finite filling, the asymptotic behaviors of superfluid density can be captured by a parabolic function of filling factor. Further more, when the filling is in flat band, the superfluid density shows a logarithmic singularity as the interaction approaches zero. In addition, there exist three undamped collective modes for strong interactions. The lowest excitation is gapless phonon, which is characterized by the total density oscillations. The two others are gapped Leggett modes, which correspond relative density fluctuations between sublattices. The collective modes are also reflected in the two-particle spectral functions by sharp peaks. Further more, it is found that the two-particle spectral functions satisfy an exact sum-rule, which is directly related to the filling factor (or density of particle). The sum-rule of the spectral functions may be useful to distinguish the hole-doped or particle-doped superfluid (superconductor) in experiments.

show abstract

Leggett collective excitations in a two-band Fermi superfluid at finite temperatures

Cited by 13 publications

References 29 publications

Superfluid density and collective modes of fermion superfluid in dice lattice

Superfluid density and collective modes of fermion superfluid in dice lattice

Superfluid properties of an ultracold Fermi gas with an orbital Feshbach resonance in the BCS-BEC crossover region

Superfluid Density and Collective Modes of Fermion Superfluid in Dice Lattice

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