Unitary Fermi Supersolid: The Larkin-Ovchinnikov Phase

Bulgac, Aurel; Forbes, Michael McNeil

doi:10.1103/physrevlett.101.215301

Cited by 114 publications

(155 citation statements)

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“…1(b) we contrast the appearance of local polarization p( r) = (ρ ↑ −ρ ↓ )/(ρ ↑ +ρ ↓ ) in the partially polarized regions of the P-SF and P-N states. We note that in [24], the strong oscillations displayed in p( r) were observed to survive the effects of fluctuations. One pleasant surprise of our results was the radial alignment of the nodes of the FFLO phase shown in Fig.…”

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confidence: 98%

“…Furthermore, recent results suggest that the inclusion of fluctuations, neglected in mean-field formulations, should make the P-SF state even more stable [24]. Thus, we expect that if the system converges to a shortened state, it will choose the P-SF state.…”

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confidence: 99%

“…Although an intriguing LDA treatment which phenomenologically includes a surface energy correction has been able to account for the shape of the distortions [21], further studies reveal that this model is not consistent with a microscopic calculation of the surface tension [22]. On the other hand, recent studies employing variational techniques in isotropic geometries [23,24] have shown that the region of stability for the FFLO state is much larger than originally predicted [25]. Until now, a fully self-consistent treatment in anistropic geometries with realistic particle numbers, has been well out of reach despite its relevance here and in a wide variety of other physical systems.…”

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Concomitant modulated superfluidity in polarized Fermi gases

et al. 2011

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Recent groundbreaking experiments studying the effects of spin polarization on pairing in unitary Fermi gases encountered mutual qualitative and quantitative discrepancies which seem to be a function of the confining geometry. Using novel numerical algorithms we study the solution space for a 3-dimensional fully self-consistent formulation of realistic systems with up to 10 5 atoms. A study of the three types of solutions obtained demonstrates a tendency towards metastability as the confining geometry is elongated. One of these solutions, which is consistent with Rice experiments at high trap aspect ratio, supports a state strikingly similar to the long sought Fulde-Ferrel-Larkin-Ovchinnikov state. Our study helps to resolve the long-standing controversy concerning the discrepancies between the findings from two different experimental groups and highlights the versatility of actual-size numerical calculations for investigating inhomogeneous fermionic superfluids. [3]. Primarily due to lack of sufficient experimental evidence, the issue remains largely unresolved even though it is central to many forms of matter such as superconductors, neutron stars and color superfluids in the quark-gluon plasma [3]. Ultra-cold samples of two component degenerate Fermi gases [6][7][8][9][10] have reenergized the debate because of their exquisite controllability.In this paper, we focus on apparently contradictory results on spin-imbalanced unitary Fermi gases from recent experiments between two leading groups [7][8][9][10]. In both experiments it was observed that, consistent with earlier predictions [1,2], the trapped superfliud responds to polarization by phase separating into an inner core with negligible polarization surrounded by a polarized outer shell. However, the Rice experiments [8,9] performed in cigar-shaped traps with total particle numbers N ∼ 10 5 observed a significant and unexpected deformation of the central superfluid core, indicating a clear violation of the local density approximation (LDA). In addition, these results also suggest a much higher superfluid to normal (Chandrasekhar-Clogston) transition than the MIT experiments [7,10] in which no deformations were observed. The excellent quantitative agreement with theory [11,12] for the MIT experiments conducted at much lower trap aspect ratio and with higher particle numbers N ∼ 10 6 , hints that there might be unexpected physics at work in the Rice experiment. In addition, the concurrence of experiments performed in Paris [13] with the MIT experiments also suggest a crucial role of the trapping geometry. This impasse has inspired speculation about the possible role of exotic phases such as the FFLO state in the observed discrepancies, and stirred much discussion and debate over the past few years by the cold atom community.The apparent contradiction between the Rice and MIT experiments reflects theoretical difficulties within trapped geometries: since the effective chemical potential (µ) varies in space, several phases may co-exist within a trapped sample. ...

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Concomitant modulated superfluidity in polarized Fermi gases

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“…It would also be interesting to investigate the existence of exotic phases such as the FFLO state, expected to be stable on the BCS side of the resonance (in a rather small window between the Fermi liquid and super uid states). The signatures of these states on the equation of state are expected to be rather small [229,230] and would require to improve the precision of our measurement or combine it with the measurement of other observables such as density correlations/ uctuations [231,230]. ‡ ‡ Recently the rst correction to (5.19) was obtained analytically [227]:…”

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confidence: 99%

Thermodynamics of Ultracold Fermi Gases

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Chevy

et al. 2010

Latin America Optics and Photonics Conference

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“…The Fermi gases are also free of disorder and all experimental parameters are highly controllable. These advantages have sparked tremendous recent interest in exploring FFLO physics in spin-imbalanced Fermi gases [18][19][20][21][22][23][24][25][26][27][28]. However, the FFLO phase only exists in a narrow parameter regime in 3D due to the Pauli depairing effect [18,22,23].…”

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Route to observable Fulde-Ferrell-Larkin-Ovchinnikov phases in three-dimensional spin-orbit-coupled degenerate Fermi gases

et al. 2013

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The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase was first predicted in 2D superconductors about 50 years ago, but so far unambiguous experimental evidences are still lacked. The recently experimentally realized spin-imbalanced Fermi gases may potentially unveil this elusive state, but require very stringent experimental conditions. In this Letter, we show that FFLO phases may be observed even in a 3D degenerate Fermi gas with spin-orbit coupling and in-plane Zeeman field. The FFLO phase is driven by the interplay between asymmetry of Fermi surface and superfluid order, instead of the interplay between magnetic and superconducting order in solid materials. The predicted FFLO phase exists in a giant parameter region, possesses a stable long-range superfluid order due to the 3D geometry, and can be observed with experimentally already achieved temperature (T ∼ 0.05EF ), thus opens a new fascinating avenue for exploring FFLO physics. The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, characterized by Cooper pairs with finite total momentum and spatially modulated order parameters, was predicted to exist in certain region of 2D superconductors in high Zeeman fields [1][2][3]. This fascinating state arises from the interplay between magnetic and superconducting order, and now is a central concept for understanding many exotic phenomena in different physics branches [4][5][6][7][8][9][10][11][12]. Despite tremendous experimental and theoretical efforts in the past five decades, there is still no unambiguous experimental evidence for FFLO states [11]. The experimental difficulty may arise from several different aspects, such as the depairing of Cooper pairs due to orbital or Pauli effects in strong magnetic fields and unavoidable disorder effects in solid state materials.The recent experimental realization of spin-imbalanced Fermi gases [13][14][15][16][17] provides a new excellent platform for exploring FFLO physics. In Fermi gases, the effective Zeeman field is generated through the population imbalance between two spins, therefore the orbital effects (e.g., vortices induced by the magnetic field) are absent even in 3D. The Fermi gases are also free of disorder and all experimental parameters are highly controllable. These advantages have sparked tremendous recent interest in exploring FFLO physics in spin-imbalanced Fermi gases [18][19][20][21][22][23][24][25][26][27][28]. However, the FFLO phase only exists in a narrow parameter regime in 3D due to the Pauli depairing effect [18,22,23]. Furthermore, the free energy difference between the FFLO state and the BCS superfluid is extremely small. As a result, only the transition from the BCS superfluid to the normal gas [13][14][15] has been observed in experiments in 3D spin-imbalanced Fermi gases. Current experimental and theoretical efforts on the FFLO state have focused on low dimensions (1D or 2D) [29][30][31][32][33], where quantum and thermal (at finite temperature) fluctuations may become crucial and the physics is much more complicated [34][35][36].In this Lett...

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Unitary Fermi Supersolid: The Larkin-Ovchinnikov Phase

Cited by 114 publications

References 42 publications

Concomitant modulated superfluidity in polarized Fermi gases

Concomitant modulated superfluidity in polarized Fermi gases

Thermodynamics of Ultracold Fermi Gases

Route to observable Fulde-Ferrell-Larkin-Ovchinnikov phases in three-dimensional spin-orbit-coupled degenerate Fermi gases

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