Stability of Spin-Orbit Coupled Fermi Gases with Population Imbalance

Iskin, M.; Subaşı, A. L.

doi:10.1103/physrevlett.107.050402

Cited by 109 publications

(201 citation statements)

References 23 publications

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“…A considerable amount of effort has been devoted to the characterization of multiple exotic superfluid phases, which can emerge in various configurations of dimensionality and forms of SOC [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Among these works, the investigation in low-dimensional systems is of particular interest, partly due to the possibility to stabilize various exotic, in many cases topologically nontrivial, pairing states.…”

Section: Introductionmentioning

confidence: 99%

Effective Hamiltonians for quasi-one-dimensional Fermi gases with spin-orbit coupling

Zhang

2013

Phys. Rev. A

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We derive one-dimensional effective Hamiltonians for spin-orbit coupled Fermi gases confined in quasi-one-dimensional trapping potentials. For energy regime around the two-body bound state energy, the effective Hamiltonian takes a two-channel form, where the population in transverse excited levels are described by dressed molecules in the closed channel. For energy regime slightly above the continuum threshold, the effective Hamiltonian takes a single-channel form, where low-energy physics is governed by the one-dimensional interacting strength determined by three-dimensional scattering length and transverse confinement. We further discuss the effect of spin-orbit coupling and effective Zeeman field on the position of confinement-induced resonances, and show that these resonances can be understood as Feshbach resonances between the threshold of the transverse ground state and the two-body bound state associated with the transverse excited states. We expect that the shift of confinement-induced resonances can be observed under present experimental technology at attainable temperatures.

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Section: Introductionmentioning

confidence: 99%

Effective Hamiltonians for quasi-one-dimensional Fermi gases with spin-orbit coupling

Zhang

2013

Phys. Rev. A

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“…Recently the BCS-BEC crossover physics of SO coupled Fermi gases with perpendicular Zeeman fields has been intensively investigated with the goal of realizing topological superfluids [40][41][42][43] and the associated Majorana fermions [44][45][46]. However, regular BCS superfluids, instead of FFLO states, are energetically preferred for perpendicular Zeeman field because of the centrally symmetric Fermi surface.…”

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confidence: 99%

“…(2) the bare interaction strength g should be regularized in terms of the s-wave scattering length a s [41,43],…”

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confidence: 99%

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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“…Their utility comes from their tunability [1] which allows the dimensionality, band structure, interaction strength, and spin imbalance to be freely varied. With these various parameters one can, in principle, simulate a number of important condensed matter systems ranging from preformed pair and related effects in the high T c cuprates [2-4] to intrinsic topological superfluids [5][6][7] and other exotic pairing states.In this paper we focus on recent experiments [8,9] of two-dimensional (2D) spin-imbalanced Fermi gases. These address the interesting conflict between the tendency towards enhanced pairing (which is associated with two dimensionality [10]), and spin imbalance which acts to greatly undermine pairing.…”

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confidence: 99%

mentioning

confidence: 99%

Two-dimensional spin-imbalanced Fermi gases at nonzero temperature: Phase separation of a noncondensate

Boyack

Levin

2016

Phys. Rev. A

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We study a trapped two-dimensional spin-imbalanced Fermi gas over a range of temperatures. In the moderate temperature regime, associated with current experiments, we find reasonable semiquantitative agreement with the measured density profiles as functions of varying spin imbalance and interaction strength. Our calculations show that, in contrast to the three-dimensional case, the phase separation which appears as a spin balanced core, can be associated with non-condensed fermion pairs. We present predictions at lower temperatures where a quasi-condensate will first appear, based on the pair momentum distribution and following the protocols of Jochim and collaborators. While these profiles also indicate phase separation, they exhibit distinctive features which may aid in identifying the condensation regime.Ultracold Fermi gases are a valuable resource for learning about highly correlated superfluids. Their utility comes from their tunability [1] which allows the dimensionality, band structure, interaction strength, and spin imbalance to be freely varied. With these various parameters one can, in principle, simulate a number of important condensed matter systems ranging from preformed pair and related effects in the high T c cuprates [2-4] to intrinsic topological superfluids [5][6][7] and other exotic pairing states.In this paper we focus on recent experiments [8,9] of two-dimensional (2D) spin-imbalanced Fermi gases. These address the interesting conflict between the tendency towards enhanced pairing (which is associated with two dimensionality [10]), and spin imbalance which acts to greatly undermine pairing. These imbalance effects are believed [11] to have related effects in studies of color superconductivity and quark-gluon plasmas. In condensed matter systems, lower dimensional imbalanced superfluids are thought to be ideal for observing more exotic phases, such as the elusive LOFF state [12], or algebraic order [13,14].The approach we use has been rather successful in addressing 2D low temperature quasi-condensation [15] in balanced gases. In this paper we present predictions for future very low temperature experiments on spinimbalanced gases. Importantly, our calculations, which find no true long range order, are consistent with the Mermin-Wagner theorem [16]. Following the experiments of Jochim and collaborators [17,18], we show how quasicondensation is reflected in the pair-momentum distribution which has a strong peak at low momentum. This peak, which we study throughout the crossover from BCS to BEC, disappears somewhat abruptly at a fixed temperature, T qc , which denotes quasi-condensation. We find T qc varies only weakly with the polarization.A central finding in this paper is that 2D spinimbalanced systems in a trap exhibit a new form of phase separation involving non-condensed pairs appearing primarily in the center region of the trap. This is to be contrasted with 3D gases [19,20] where the phase separation is associated with a true condensate. In the 2D polarized case, because almost all the ...

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Stability of Spin-Orbit Coupled Fermi Gases with Population Imbalance

Cited by 109 publications

References 23 publications

Effective Hamiltonians for quasi-one-dimensional Fermi gases with spin-orbit coupling

Effective Hamiltonians for quasi-one-dimensional Fermi gases with spin-orbit coupling

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

Two-dimensional spin-imbalanced Fermi gases at nonzero temperature: Phase separation of a noncondensate

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