Trionic phase of ultracold fermions in an optical lattice: A variational study

Rapp, Ákos; Hofstetter, Walter; Zaránd, Gergely

doi:10.1103/physrevb.77.144520

Cited by 71 publications

(68 citation statements)

References 37 publications

(71 reference statements)

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“…It was argued that for atoms with a weak attractive interaction two of the three colors form Cooper pairs, yielding a color superfluid (CSF). As the strength of the attractive interaction increases, there is a quantum phase transition from the CSF state to the trionic state, where three atoms with different colors form singlet bound states [10,11].In contrast to the detailed investigations that have been undertaken at zero temperature, little information is available about the finite-temperature properties. Recently, fermionic atoms with a balanced population of three different hyperfine states were successfully created [12].…”

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confidence: 99%

“…It has been shown that three-component (colors) fermionic atoms exhibit characteristic features. Their properties in optical lattices at zero temperature have been studied theoretically [8,9,10,11]. It was argued that for atoms with a weak attractive interaction two of the three colors form Cooper pairs, yielding a color superfluid (CSF).…”

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Finite-temperature properties of attractive three-component fermionic atoms in optical lattices

Suga

2009

Phys. Rev. A

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We investigate the finite-temperature properties of attractive three-component (colors) fermionic atoms in optical lattices using a self-energy functional approach. As the strength of the attractive interaction increases in the low-temperature region, we observe a second-order transition from a Fermi liquid to a color superfluid (CSF), where atoms from two of the three colors form Cooper pairs. In the strong attractive region, we observe a first-order transition from a CSF to a trionic state, where three atoms with different colors form singlet bound states. A crossover between a Fermi liquid and a trionic state is observed in the high-temperature region. We present a phase diagram covering zero to finite temperatures. We demonstrate that the CSF transition temperature is enhanced by the anisotropy of the attractive interaction. The study of cold fermionic atoms has attracted considerable attention. Fascinating aspects of many-body effects have been revealed in various phenomena. A crossover between a BCS-type superfluid and BoseEinstein condensation (BEC) was observed by controlling the strength of the attractive interaction using Feshbach resonances [1,2,3,4,5,6]. A superfluid-insulator transition was observed for 6 Li fermionic atoms in an optical lattice [7]. These phenomena with a highly tuned attractive interaction may be difficult to observe in condensed matter physics. One can expect further that the cold fermionic atoms show the novel phenomena beyond those observed in the condensed matter. It has been shown that three-component (colors) fermionic atoms exhibit characteristic features. Their properties in optical lattices at zero temperature have been studied theoretically [8,9,10,11]. It was argued that for atoms with a weak attractive interaction two of the three colors form Cooper pairs, yielding a color superfluid (CSF). As the strength of the attractive interaction increases, there is a quantum phase transition from the CSF state to the trionic state, where three atoms with different colors form singlet bound states [10,11].In contrast to the detailed investigations that have been undertaken at zero temperature, little information is available about the finite-temperature properties. Recently, fermionic atoms with a balanced population of three different hyperfine states were successfully created [12]. The temperature at which these atoms were realized was T /T F ∼ 0.37 [12], where T F is the Fermi temperature. Studies of the finite-temperature properties are thus indispensable. In particular, the stabilities of the CSF and trionic phases against thermal fluctuations are important in terms of observing these novel states in experiments.In this paper, we investigate fermionic atoms with three different colors (α = 1, 2, 3) in optical lattices at zero and finite temperatures. Using a self-energy functional approach (SFA) [13,14], we elucidate characteristics of the CSF, trionic, and Fermi liquid states, and study the phase transition and crossover between them. In accordance with the conventional mod...

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Finite-temperature properties of attractive three-component fermionic atoms in optical lattices

Suga

2009

Phys. Rev. A

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“…As an interesting consequence of these many-body corrections we predict in a spatially varying confining potential (typically harmonic trap) the appearance of superfluid shell structures even in the absence of population imbalance (polarization) of the components. These shell structures are due to many-body effects only and therefore fundamentally different from earlier predictions of shell structures due to population, mass, or trapping potential imbalance [23,24] We also point out that many body effects due to the third component provide a new way to tune the effective interaction between the two other fermions and that this contribution can dominate over the usual GM contribution.Earlier, intriquing results have been found experimentally for the critical temperature of iron-based multiband superconductors [25] and degenerate three-component Fermi gases have been studied theoretically in a lattice [26,27]. Furthermore, pairing [23,28,29], stability [30], and breached pairing [31] have recently been studied in a three-component fermionic mixtures.…”

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Induced Interactions and the Superfluid Transition Temperature in a Three-Component Fermi Gas

et al. 2009

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We study many-body contributions to the effective interaction between fermions in a threecomponent Fermi mixture. We find that effective interactions induced by the third component can lead to a phase diagram different from that predicted if interactions with the third component are neglected. As a result, in a confining potential a superfluid shell structure can arise even for equal populations of the components. We also find a critical temperature for the BCS transition in a 6 Li mixture which can deviate strongly from the one in a weakly interacting two-component system.By using Feshbach resonances to change the effective interaction between ultracold atoms several groups have probed the crossover from the Bardeen-CooperSchrieffer (BCS) superfluid to a Bose-Einstein condensate of molecules [1][2][3][4][5][6][7][8][9][10]. Studies of the crossover have provided important insights into fermionic superfluids around the unitarity limit of strong interactions. Importantly, it has become experimentally feasible to study also more complicated mixtures than Fermi gases with two different atomic internal states. Bose-Fermi mixtures [11,12] and Bose-Einstein condensates with many components have been created using many different setups [13,14]. Also, heteronuclear Fermi-Fermi mixtures [15,16] and even heteronuclear Fermi-Fermi-Bose mixtures [17] have been recently demonstrated. In yet another breakthrough a three-component Fermi mixture of atoms in the three lowest hyperfine states of 6 Li [18,19] has also been demonstrated. Such multicomponent systems have some intriguing similarities with quark matter counterparts where color superconductivity may appear [20].The purpose of this Letter is to explore how the induced interactions due to the third component modify the expected behavior of three-component mixtures. This is important because, depending on parameters, the many-body effects can change the effective interaction between atoms substantially and on occasion even change the relative magnitudes of couplings between different components. Such changes imply that phase diagrams predicted using only two-body scattering properties can be incorrect. Also, even when the corrections to the effective interactions are weak, they can cause large changes to the critical temperature for the BCS transition. Indeed, for a two component system Gorkov and MelikBarkhudarov (GM) showed [21] that the perturbative correction to the effective interaction can reduce the critical temperature by a constant factor of (4e) 1/3 ≈ 2.22 in the weak-coupling limit. Also in spin-density imbalanced systems such corrections have been shown to have a considerable effect [22]. Here we will analyze the effects of analogous corrections on the three component system and find important changes to the GM result. As an interesting consequence of these many-body corrections we predict in a spatially varying confining potential (typically harmonic trap) the appearance of superfluid shell structures even in the absence of population imbalance (polarization)...

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“…How will pairing occur in such a system: Will the individual components compete, and only two of them form pairs, while the third component remains a spectator, or will the lowest-energy state of the system be a three-body bound state [19,20,21]? There are predictions for a phase transition between a superfluid and trionic phase in optical lattices, which can be treated analogous to baryon formation in QCD [22]. Furthermore, as the Fermi pressure is lower than in a twocomponent mixture of equal density, the stability of such a gas in the case of resonant two-particle interactions is still a controversial topic [23,24].…”

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Collisional Stability of a Three-Component Degenerate Fermi Gas

et al. 2008

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We report on the creation of a degenerate Fermi gas consisting of a balanced mixture of atoms in three different hyperfine states of 6 Li. This new system consists of three distinguishable Fermions with different and tunable interparticle scattering lengths a12, a13 and a23. We are able to prepare samples containing 5 · 10 4 atoms in each state at a temperature of about 215 nK, which corresponds to T /TF ≈ 0.37. We investigated the collisional stability of the gas for magnetic fields between 0 and 600 G and found a prominent loss feature at 130 G. From lifetime measurements we determined three-body loss coefficients, which vary over nearly three orders of magnitude.

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Trionic phase of ultracold fermions in an optical lattice: A variational study

Cited by 71 publications

References 37 publications

Finite-temperature properties of attractive three-component fermionic atoms in optical lattices

Finite-temperature properties of attractive three-component fermionic atoms in optical lattices

Induced Interactions and the Superfluid Transition Temperature in a Three-Component Fermi Gas

Collisional Stability of a Three-Component Degenerate Fermi Gas

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