Fermi surface deformations and pairing in mixtures of dipolar and non-dipolar fermions

Baarsma, J. E.; Törmä, P.

doi:10.48550/arxiv.1612.07953

Cited by 4 publications

(5 citation statements)

References 45 publications

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“…The ground-state [39,40] and the dynamic properties of such systems have been systematically investigated theoretically and numerically in the collisionless regime [41][42][43], in the hydrodynamic regime [44,45], as well as in the whole collisional range from one limiting case to the other [46,47]. The FS deformation was also recently theoretically studied in mixtures of dipolar and non-dipolar fermions [48], as well as in the presence of a weak lattice confinement [49].…”

Section: Introductionmentioning

confidence: 99%

Ground state of an ultracold Fermi gas of tilted dipoles in elongated traps

et al. 2018

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Many-body dipolar effects in Fermi gases are quite subtle as they energetically compete with the large kinetic energy at and below the Fermi surface (FS). Recently it was experimentally observed in a sample of erbium atoms that its FS is deformed from a sphere to an ellipsoid due to the presence of the anisotropic and long-range dipole-dipole interaction Aikawa et al (2014 Science 345 1484). Moreover, it was suggested that, when the dipoles are rotated by means of an external field, the FS follows their rotation, thereby keeping the major axis of the momentum-space ellipsoid parallel to the dipoles. Here we generalise a previous Hartree-Fock mean-field theory to systems confined in an elongated triaxial trap with an arbitrary orientation of the dipoles relative to the trap. With this we study for the first time the effects of the dipoles' arbitrary orientation on the ground-state properties of the system. Furthermore, taking into account the geometry of the system, we show how the ellipsoidal FS deformation can be reconstructed, assuming ballistic expansion, from the experimentally measurable real-space aspect ratio after a free expansion. We compare our theoretical results with new experimental data measured with erbium Fermi gas for various trap parameters and dipole orientations. The observed remarkable agreement demonstrates the ability of our model to capture the full angular dependence of the FS deformation. Moreover, for systems with even higher dipole moment, our theory predicts an additional unexpected effect: the FS does not simply follow rigidly the orientation of the dipoles, but softens showing a change in the aspect ratio depending on the dipoles' orientation relative to the trap geometry, as well as on the trap anisotropy itself. Our theory provides the basis for understanding and interpreting phenomena in which the investigated physics depends on the underlying structure of the FS, such as fermionic pairing and superfluidity.

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Section: Introductionmentioning

confidence: 99%

Ground state of an ultracold Fermi gas of tilted dipoles in elongated traps

et al. 2018

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“…The resonances predicted here have a wide range of possible applications. The wider resonances are very suitable for tuning interspecies interactions, both to achieve properties desirable for formation of dual degenerate gases and to investigate the novel properties of mixtures of dipolar and non-dipolar species [42][43][44]. Further tuning may be achieved by selecting from the wide variety of isotopic combinations available.…”

Section: Discussionmentioning

confidence: 99%

“…High densities can be produced, and for suitable isotopic combinations it is likely that mixed degenerate gases with controllable interactions can be formed. They therefore provide an ideal platform for investigating the rich phase behavior expected in such mixtures, including superfluidity and supersolidity [42], dipolar droplet properties [43] and Fermi surface deformation [44].…”

mentioning

confidence: 99%

Prospects of forming high-spin polar molecules from ultracold atoms

Frye,

Cornish,

Hutson

2019

Preprint

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“…The experimental observation of BCS-BEC crossover in ultracold atomic gases [19][20][21][22][23][24][25] might be a paramount example of this. Furthermore, recent successful achievements of quantum degenerate state of polar molecules and magnetic atoms [26][27][28][29][30][31][32] have offered alternative scenarios, in which the long-range and anisotropic characteristic of the dipole-dipole interaction (DDI), as well as its high controllability via external fields, provided new avenues to the observation of topological states [33,34], density waves [35][36][37][38][39][40][41][42][43][44][45][46], and exotic superfluidity [47][48][49][50]. For instance, engineering layered structures of dipolar fermions offer a very powerful platform to study interlayer superfluidity, thanks to the attractive component of the interlayer interactions.…”

Section: Introductionmentioning

confidence: 99%

Interplay of interlayer pairing and many-body screening in a bilayer of dipolar fermions

Mazloom¹,

Abedinpour²

2018

Phys. Rev. B

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In a bilayer system of fermionic dipoles, a full control over the strength of the attractive interactions between two layers leads to the BCS-BEC crossover. Here, using the BCS mean field theory, we study such a crossover in symmetric bilayers of ultracold dipolar fermions with their dipole moments being perpendicular to layers. In particular, we investigate how the pairing between two layers and the many-body screening of interlayer interaction affect each other. We compare results for pairings obtained with three different approximations for the interlayer interactions namely, bare dipoledipole interaction, the random-phase approximation for screening obtained in the normal phase, and the self-consistent superfluid phase screening within the random-phase approximation. We find that at weak couplings the screening further suppresses the pairing while at strong couplings, the screening would be suppressed due to the pairing gap in the quasi-particle spectrum. Therefore a self-consistent treatment of both screening and pairing on equal footings is necessary for obtaining a correct picture of the phase diagram and order parameter at both small and large layer spacings and densities. We also notice that the highly speculated density-wave instability in bilayers with the parallel polarization of dipoles in two layers is simply an artifact of the incorrect screening scheme.

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Fermi surface deformations and pairing in mixtures of dipolar and non-dipolar fermions

Cited by 4 publications

References 45 publications

Ground state of an ultracold Fermi gas of tilted dipoles in elongated traps

Ground state of an ultracold Fermi gas of tilted dipoles in elongated traps

Prospects of forming high-spin polar molecules from ultracold atoms

Interplay of interlayer pairing and many-body screening in a bilayer of dipolar fermions

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