Low-Lying Excitation Modes of Trapped Dipolar Fermi Gases: From Collisionless to Hydrodynamic Regime

Waechtler, F.; Lima, Aristeu R. P.; Pelster, Axel

doi:10.48550/arxiv.1311.5100

Cited by 4 publications

(16 citation statements)

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“…In the Hartree-Fock formalism, the FSD comes from the exchange interaction among fermions, known as the Fock term ( [12,16] and Supplementary Materials). Our observations agree very well with parameter-free calculations based on the Hartree-Fock theory [12,15,17]. We demonstrate that the degree of deformation, related to the nematic susceptibility in the liquidcrystal vocabulary, can be controlled by varying the Fermi energy of the system and vanishes at high temperatures.…”

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confidence: 86%

“…Recently, Fermi gases with anisotropic interactions have attracted remarkable attention in the context of p-wave superfluidity [9,10] and dipolar physics [11]. Many theoretical studies have focused on dipolar Fermi gases, predicting the existence of a deformed FS [12][13][14][15][16][17]. These studies also include an extension of the Landau Fermi-liquid theory to the case of anisotropic interactions [18].…”

mentioning

confidence: 99%

“…In our experiments, the DDI is acting even during the expansion and could potentially mask the observation of the FSD. We evaluate the effect of the nonballistic expansion (NBE) by performing numerical calculations based on the Hartree-Fock mean-field theory at zero temperature and the Boltzmann-Vlasov equation for expansion dynamics [15,17] (Supplementary Materials). In Fig.…”

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confidence: 99%

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Observation of Fermi surface deformation in a dipolar quantum gas

Aikawa

Baier

Frisch

et al. 2014

Science

103

159

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The deformation of a Fermi surface is a fundamental phenomenon leading to a plethora of exotic quantum phases. Understanding these phases, which play crucial roles in a wealth of systems, is a major challenge in atomic and condensed-matter physics. Here, we report on the observation of a Fermi surface deformation in a degenerate dipolar Fermi gas of erbium atoms. The deformation is caused by the interplay between strong magnetic dipole-dipole interaction and the Pauli exclusion principle. We demonstrate the many-body nature of the effect and its tunability with the Fermi energy. Our observation provides basis for future studies on anisotropic many-body phenomena in normal and superfluid phases.PACS numbers: 03.75. Ss, 37.10.De, 51.60.+a, 67.85.Lm The Fermi-liquid theory, formulated by Landau in the late 50's, is one of the most powerful tools in modern condensedmatter physics [1]. It captures the behavior of interacting Fermi systems in the normal phase, such as electrons in metals and liquid 3 He [2]. Within this theory the interaction is accounted by dressing the fermions as quasi-particles with an effective mass and an effective interaction. The ground state is the so-called Fermi sea, in which the quasi-particles fill one-by-one all the states up to the Fermi momentum, k F . The Fermi surface (FS), which separates occupied from empty states in k-space, is a sphere of radius k F for isotropically interacting fermions in uniform space. The FS is crucial for understanding system excitations and Cooper pairing in superconductors. When complex interactions act, the FS can get modified. For instance, strongly-correlated electron systems violates the Fermi-liquid picture, giving rise to a deformed FS, which spontaneously breaks the rotational invariance of the system [3]. Symmetry-breaking FSs have been studied in connection with electronic liquid crystal phases [4] and Pomeranchuk instability [5] in solid state systems. Particularly relevant is the nematic phase, in which anisotropic behaviors spontaneously emerge and the system acquires an orientational order, while preserving its translational invariance. This exotic phase has recently been observed by transport and thermodynamics studies in ruthenates [6], in high-transitiontemperature superconductors such as cuprates [7], and in other systems [3].A completely distinct approach to study FSs is provided by ultracold quantum gases. These systems are naturally free from impurities and crystal structures, realizing a situation close to the ideal uniform case. Here, the shape of the FS can directly reveal the fundamental interactions among particles. Studies of FSs in strongly interacting Fermi gases have been crucial in understanding the BEC-to-BCS crossover, where the isotropic s-wave (contact) interaction causes a broadening of the always-spherical FS [8]. Recently, Fermi gases with anisotropic interactions have attracted remarkable attention in the context of p-wave superfluidity [9, 10] and dipolar physics [11]. Many theoretical studies have focused on dipol...

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Observation of Fermi surface deformation in a dipolar quantum gas

Aikawa

Baier

Frisch

et al. 2014

Science

103

159

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“…In view of the reasonable expectation that the quasi-2D analogue of this experiment is possible, along with foreseeable studies of the collective excitations, a theoretical investigation of the collective modes is of interest. Although a variety of theoretical techniques have been used to investigate the collective excitations of trapped dFGs in three [6][7][8][9][10][11][12][13], and lower dimensional geometries [14][15][16][17], we feel that it is useful to present another, relatively unknown approach, namely, the TFvW hydrodynamic theory.…”

Section: Introductionmentioning

confidence: 99%

Collective excitations of a harmonically trapped, two-dimensional, spin-polarized dipolar Fermi gas in the hydrodynamic regime

2014

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The collective excitations of a zero-temperature, spin-polarized, harmonically trapped, twodimensional dipolar Fermi gas are examined within the Thomas-Fermi von Weizsäcker hydrodynamic theory. We focus on repulsive interactions, and investigate the dependence of the excitation frequencies on the strength of the dipolar interaction and particle number. We find that the mode spectrum can be classified according to bulk modes, whose frequencies are shifted upward as the interaction strength is increased, and an infinite ladder of surface modes, whose frequencies are independent of the interactions in the large particle limit. We argue quite generally that it is the local character of the two-dimensional energy density which is responsible for the insensitivity of surface excitations to the dipolar interaction strength, and not the precise form of the equation of state. This property will not be found for the collective excitations of harmonically trapped, dipolar Fermi gases in one and three dimensions, where the energy density is manifestly nonlocal.

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“…In contrast, for a rapidly rotating 2D system of dipolar fermions the Wigner crystal phase is possibly the ground state for low densities, while for higher densities it turns into a Laughlin liquid state [43,44]. Further studies focused on finitetemperature effects [27,[45][46][47][48], dynamical properties in the collisionless and hydrodynamic regimes [49][50][51][52][53][54][55], bilayer configurations [56][57][58][59], and quench dynamics [60]. However, less attention has been paid to the quasiparticle properties in the Fermi liquid phase beyond the meanfield level.…”

Section: Introductionmentioning

confidence: 99%

Second-order interaction corrections to the Fermi surface and the quasiparticle properties of dipolar fermions in three dimensions

et al. 2015

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We calculate the renormalized Fermi surface and the quasiparticle properties in the Fermi liquid phase of three-dimensional dipolar fermions to second order in the dipole-dipole interaction. Using parameters relevant to an ultracold gas of erbium atoms, we find that the second-order corrections typically renormalize the Hartree-Fock results by less than 1%. On the other hand, if we use the second-order correction to the compressibility to estimate the regime of stability of the system, the point of instability is already reached for a significantly smaller interaction strength than in the Hartree-Fock approximation.

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Low-Lying Excitation Modes of Trapped Dipolar Fermi Gases: From Collisionless to Hydrodynamic Regime

Cited by 4 publications

References 2 publications

Observation of Fermi surface deformation in a dipolar quantum gas

Observation of Fermi surface deformation in a dipolar quantum gas

Collective excitations of a harmonically trapped, two-dimensional, spin-polarized dipolar Fermi gas in the hydrodynamic regime

Second-order interaction corrections to the Fermi surface and the quasiparticle properties of dipolar fermions in three dimensions

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