Instability of superfluid Fermi gases induced by a rotonlike density mode in optical lattices

Yunomae, Yoshihiro; Yamamoto, Daisuke; Danshita, Ippei; Yokoshi, Nobuhiko; Tsuchiya, Shunji

doi:10.1103/physreva.80.063627

Cited by 21 publications

(53 citation statements)

References 55 publications

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“…We suggest that this DI leads to the formation of density waves with ordering vectors k ≃ ±0.3π and ±0.5π. While this type of DI has been previously found in the presence of off-site interactions [28,[41][42][43], this is the first example of such a DI in the standard Bose-Hubbard model only with the on-site interaction. …”

Section: Critical Momenta In Homogeneous Optical Latticessupporting

confidence: 48%

Detecting the superfluid critical momentum of Bose gases in optical lattices through dipole oscillations

Saito

Danshita²,

Ozaki³

et al. 2012

Phys. Rev. A

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We study stability of superflow of Bose gases in optical lattices by analyzing the Bose-Hubbard model within the Gutzwiller mean-field approximation. We calculate the excitation spectra of the homogeneous Bose-Hubbard model at unit filling to determine the critical momenta for the Landau and dynamical instabilities. These two critical momenta are shown to approach each other when the on-site interaction increases towards the Mott transition point. In order to make a direct connection with realistic experiments, we next take into account a parabolic trapping potential and compute the real-time dynamics of dipole oscillations induced by suddenly displacing the trap center. We consider the following two cases: standard softcore bosons, whose interparticle interactions include the on-site one only, and hardcore bosons with long-range dipole-dipole interactions. For both cases, we show that the dipole oscillation is significantly damped when the maximum local momentum exceeds a certain threshold, which quantitatively agrees with the critical momentum for the dynamical instability in the homogeneous system. In the case of dipolar hardcore bosons, the dynamical instability of dipole oscillations leads to the formation of checkerboard density waves in the superfluid phase near the boundary to the supersolid phase.

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Section: Critical Momenta In Homogeneous Optical Latticessupporting

confidence: 48%

Detecting the superfluid critical momentum of Bose gases in optical lattices through dipole oscillations

Saito

Danshita²,

Ozaki³

et al. 2012

Phys. Rev. A

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“…If the roton gap ∆ can be decreased by changing the system parameters, the softening of the roton mode can eventually lead to an instability. This instability scenario is encountered also in many other branches of quantum physics, including strongly correlated Fermions [10], quantum Hall systems [11], and Bose-Einstein condensates with long range interactions [12][13][14]. The roton instability is characterized by unstable modes with wavevector lengths close to the roton minimum k 0 .…”

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confidence: 93%

Rotonlike Instability and Pattern Formation in Spinor Bose-Einstein Condensates

Matuszewski

2010

Phys. Rev. Lett.

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We show that metastable phases of an antiferromagnetic spin-1 condensate in a simple model with pure contact interactions can exhibit a rotonlike minimum in the excitation spectrum. The introduction of magnetic field gives rise to the instability of roton modes, which can lead to spontaneous emergence of regular periodic, polygonal, polyhedral or crystalline patterns, as shown in numerical simulations within the truncated Wigner approximation. An explanation of the occurrence of rotonlike instability is given based on the energy and spin conservation laws.PACS numbers: 03.75. Kk, 03.75.Mn, 67.85.De, 67.85.Fg Bose-Einstein condensates with spin degrees of freedom [1] attracted in recent years great interest due to the unique possibility of exploring fundamental concepts of quantum mechanics in a remarkably controllable and tunable environment. The ability to generate spin squeezing and entanglement [2] makes spinor Bose gases promising candidates for applications as quantum simulators [3], in quantum information [4], and for precise measurements [5]. Moreover, spinor condensates were successfully used to recreate many of the phenomena of condensed matter physics in experiments displaying an unprecedented level of control over the quantum system. In particular, spin domains [6], spin mixing [7], and spin vortices [8] were predicted and observed.The fundamental concept of a roton excitation, first introduced by Landau in the context of superfluid helium, is crucial for understanding of its physical properties [9]. It is characterized by a minimum in the spectrum of excitations occurring at a finite wavelength,. If the roton gap ∆ can be decreased by changing the system parameters, the softening of the roton mode can eventually lead to an instability. This instability scenario is encountered also in many other branches of quantum physics, including strongly correlated Fermions [10], quantum Hall systems [11], and Bose-Einstein condensates with long range interactions [12][13][14]. The roton instability is characterized by unstable modes with wavevector lengths close to the roton minimum k 0 . It was suggested that it can lead to the emergence of the peculiar supersolid state [15], and several other physical phenomena [16].Here, we show that rotonlike instability can occur in spinor Bose-Einstein condensates in a simple model with pure contact interactions. It can take place in appropriately prepared metastable states of an antiferromagnetic spin-1 condensate [17] under the influence of magnetic field. Moreover, we show that, depending on the geometry and the trapping potential, it can lead to spontaneous emergence of variety of transient ordered patterns, including polygonal, polyhedral and crystalline structures. We show that these results can be verified in experiments with 23 Na condensate, which is characterized by very weak dipolar interactions [18]. We provide an explanation for the occurrence of rotonlike instability based on energy and spin conservation laws, and demonstrate how the pattern characteristic...

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“…When K increases in this region, the roton-like excitations cause DI, which signals the transition to the CSS phase [39][40][41][42], before LI occurs. The critical value of K for this DI is plotted by the dashed-dotted green line in Fig.…”

Section: Excitation Spectra and Critical Velocitymentioning

confidence: 99%

Critical velocity of flowing supersolids of dipolar Bose gases in optical lattices

Danshita

Yamamoto

2010

Phys. Rev. A

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We study superfluidity of supersolid phases of dipolar Bose gases in two-dimensional optical lattices. We perform linear stability analyses for the corresponding dipolar Bose-Hubbard model in the hardcore boson limit to show that a supersolid can have stable superflow until the flow velocity reaches a certain critical value. The critical velocity for the supersolid is found to be significantly smaller than that for a conventional superfluid phase. We propose that the critical velocity can be used as a signature to identify the superfluidity of the supersolid phase in experiment.

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Instability of superfluid Fermi gases induced by a rotonlike density mode in optical lattices

Cited by 21 publications

References 55 publications

Detecting the superfluid critical momentum of Bose gases in optical lattices through dipole oscillations

Detecting the superfluid critical momentum of Bose gases in optical lattices through dipole oscillations

Rotonlike Instability and Pattern Formation in Spinor Bose-Einstein Condensates

Critical velocity of flowing supersolids of dipolar Bose gases in optical lattices

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