Density-wave instability in a two-dimensional dipolar Fermi gas

Yamaguchi, Yasuhiro; Sogo, T.; Ito, Toru; Miyakawa, Takuma

doi:10.1103/physreva.82.013643

Cited by 83 publications

(148 citation statements)

References 31 publications

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“…The stability of the normal phase against density fluctuations with a finite momentum (density wave instability) was investigated in RPA in Refs. [30] and -extending the discussion to finite temperatures and taking into account the deformation of the Fermi surface - [25]. It was found, that a density wave transition takes place in a broad region in the parameter space (the coupling strength and the tilting angle θ 0 ), where the system is stable against collapse.…”

Section: Introductionmentioning

confidence: 99%

“…While this perturbative approach provides reliable answers in the weak coupling regime, moderate interaction strengths require more sophisticated methods such as the Hartree-Fock approximation (HFA), which was used in Ref. [25] to obtain the spectrum of singleparticle excitations at zero and finite temperature. At zero temperature, the results were found to agree very well with the outcome of a variational approach that was initially used to study Fermi surface deformations in the 3D case [26] and adapted to the 2D case by the authors of Ref.…”

Section: Introductionmentioning

confidence: 99%

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Collective modes, stability, and superfluid transition of a quasi-two-dimensional dipolar Fermi gas

Sieberer

Baranov

2011

Phys. Rev. A

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We examine collective modes, stability, and BCS pairing in a quasi-two-dimensional gas of dipolar fermions aligned by an external field. By using the (conserving) Hartree-Fock approximation, which treats direct and exchange interactions on an equal footing, we obtain the spectrum of single-particle excitations and long wavelength collective modes (zero sound) in the normal phase. It appears that exchange interactions result in strong damping of zero sound when the tilting angle between the dipoles and the normal to the plane of confinement is below some critical value. In particular, zero sound cannot propagate if the dipoles are perpendicular to the plane of confinement. At intermediate coupling we find unstable modes that can lead either to collapse of the system or the formation of a density wave. The BCS transition to a superfluid phase, on the other hand, occurs at arbitrarily weak strengths of the dipole-dipole interaction, provided the tilting angle exceeds a critical value. We determine the critical temperature of the transition taking into account many-body effects as well as virtual transitions to higher excited states in the confining potential, and discuss prospects of experimental observations.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Collective modes, stability, and superfluid transition of a quasi-two-dimensional dipolar Fermi gas

Sieberer

Baranov

2011

Phys. Rev. A

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“…This approximation is relevant to a well-separated stack of pancakes as well. The normal phase and the collective modes of fermionic polar molecules in the strictly two-dimensional case (single-subband limit) has been recently studied by different authors [22,33,36]. Therefore, we do not discuss the intra-subband collective modes here and instead, focus on genuinely quasi-two-dimensional phenomena.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, experiments with polar molecules go beyond quantum simulation of effective theories motivated by electronic systems and aim at exploring a genuinely new domain of many-body quantum behavior, unique to dipolar interactions. Dipolar interactions can be utilized to generate long-range interactions of arbitrary shape using microwave fields [11], simulate exotic spin Hamiltonians [12,13] and are theoretically predicted to give rise to numerous interesting collective phenomena such as roton softening [14][15][16], supersolidity [17][18][19][20][21], p-wave superfluidity [22], emergence of artificial photons [23], bilayer quantum phase transitions [24], multi-layer self-assembled chains [25] for bosonic molecules, dimerization and inter-layer pairing [26,27], spontaneous inter-layer coherence [28], itinerant ferroelectricity [29], anisotropic Fermi liquid theory and anisotropic sound modes [30][31][32][33], fractional quantum Hall effect [34], Wigner crystallization [35], density-wave and striped order [36,37], biaxial nematic phase [38], topological superfluidity [39] and Z 2 topological phase [40], just to mention a few.…”

Section: Introductionmentioning

confidence: 99%

Collective phenomena in a quasi-two-dimensional system of fermionic polar molecules: Band renormalization and excitons

Babadi

Demler

2011

Phys. Rev. A

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We theoretically analyze a quasi-two-dimensional system of fermionic polar molecules in a harmonic transverse confining potential. The renormalized energy bands are calculated by solving the Hartree-Fock equation numerically for various trap and dipolar interaction strengths. The inter-subband excitations of the system are studied in the conserving time-dependent Hartree-Fock (TDHF) approximation from the perspective of lattice modulation spectroscopy experiments. We find that the excitation spectrum consists of both intersubband particle-hole excitation continuums and anti-bound excitons, arising from the anisotropic nature of dipolar interactions. The excitonic modes capture the majority of the spectral weight. We also evaluate the inter-subband transition rates in order to investigate the nature of the excitonic modes and find that they are antibound states formed from particle-hole excitations arising from several subbands. Our results indicate that the excitonic effects are present for interaction strengths and temperatures accessible in current experiments with polar molecules. I. INTRODUCTIONIn the past decade, much of the experimental and theoretical progress in the field of ultracold atoms [1][2][3] are motivated by the prospect of realizing novel strongly correlated many-body states of matter. In particular, experimental realization of quantum degenerate gases of fermionic polar molecules has witnessed a very rapid progress. By association of atoms via a Feshbach resonance to form deeply bound ultracold molecules [4,5], a nearly degenerate gas of KRb polar molecules in their rotational and vibrational ground state has been recently realized [6][7][8][9][10]. The molecules can be polarized by applying a d.c. electric field, resulting in strong dipole-dipole inter-molecular interactions.A strikingly new feature of systems of fermionic polar molecules is the anisotropy of dipolar interactions, making them unparalleled among the traditional condensed matter systems. Thus, experiments with polar molecules go beyond quantum simulation of effective theories motivated by electronic systems and aim at exploring a genuinely new domain of many-body quantum behavior, unique to dipolar interactions. Dipolar interactions can be utilized to generate long-range interactions of arbitrary shape using microwave fields [11], simulate exotic spin Hamiltonians [12,13] and are theoretically predicted to give rise to numerous interesting collective phenomena such as roton softening [14][15][16] Despite the theoretical prediction of numerous exotic quantum many-body phenomena in polar molecules, realization and observation of many of these novel predictions are still an experimental challenge. At the time this paper was written, the coldest gas of fermionic polar molecules has been realized with KRb molecules at a temperature of 1.4 T F [6-10], where T F is the Fermi temperature. The majority of the mentioned quantum phenomena require strong suppression of thermal fluctuations, i.e. strong degeneracy condition (T T F ).A major...

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“…These problems can be overcome in low-dimensional geometries where the dipolar particles are confined to either twodimensional (2D) planes or one-dimensional (1D) tubes with and without the presence of lattice potentials. A number of interesting predictions have been made for the phases of system with dipolar interactions, including exotic superfluids [15][16][17][18][19] , Luttinger liquids [20][21][22][23][24][25] , Mott insulators 26,27 , interlayer pairing [28][29][30][31] , non-trivial quantum critical points 32,33 , modified confinement-induced resonances [34][35][36][37] , roton modes and stripe instabilities [38][39][40][41][42][43][44][45] , and crystallization [46][47][48][49][50][51][52][53][54] , as well as formation of chain complexes [55][56][57][58][59][60]…”

Section: Introductionmentioning

confidence: 99%

Dipoles on a two-leg ladder

Gammelmark¹,

Zinner²

2013

Phys. Rev. B

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We study polar molecules with long-range dipole-dipole interactions confined to move on a two-leg ladder for different orientations of the molecular dipole moments with respect to the ladder. Matrix product states are employed to calculate the many-body ground state of the system as function of lattice filling fractions, perpendicular hopping between the legs, and dipole interaction strength. We show that the system exhibits zig-zag ordering when the dipolar interactions are predominantly repulsive. As a function of dipole moment orientation with respect to the ladder, we find that there is a critical angle at which ordering disappears. This angle is slightly larger than the angle at which the dipoles are non-interacting along a single leg. This behavior should be observable using current experimental techniques.

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Density-wave instability in a two-dimensional dipolar Fermi gas

Cited by 83 publications

References 31 publications

Collective modes, stability, and superfluid transition of a quasi-two-dimensional dipolar Fermi gas

Collective modes, stability, and superfluid transition of a quasi-two-dimensional dipolar Fermi gas

Collective phenomena in a quasi-two-dimensional system of fermionic polar molecules: Band renormalization and excitons

Dipoles on a two-leg ladder

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