Stable, Strongly Attractive, Two-State Mixture of Lithium Fermions in an Optical Trap

O’Hara, K. M.; Gehm, Michael E.; Granade, S. R.; Bali, Samir; Thomas, J. E.

doi:10.1103/physrevlett.85.2092

Cited by 49 publications

(47 citation statements)

References 17 publications

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“…In the second analysis we investigate 7 Li as well; however, we only do a mass scaling for the triplet potential. Our total set of 6 Li experiments comprises six data points: the zero crossing of the scattering length of a system in the two lowest hyperfine states [18,19]; in the same spin state configuration, the positions of the narrow [20] and wide [7] Feshbach resonances; and the measurement of the scattering length in the lowest and third to lowest hyperfine state [21] and the binding energy of the most weakly bound triplet state [22].…”

Section: Formation Of Fermionic Molecules Via Interisotope Feshbach Rmentioning

confidence: 99%

Formation of fermionic molecules via interisotope Feshbach resonances

2004

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We perform an analysis of recent experimental measurements and improve the lithium interaction potentials. For 6 Li a consistent description can be given. We discuss theoretical uncertainties for the position of the wide 6 Li Feshbach resonance, and we present an analytic scattering model for this resonance, based on the inclusion of a field-dependent virtual open-channel state. We predict new Feshbach resonances for the 6 Li-7 Li system, and their importance for different types of crossover superfluidity models is discussed.

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Section: Formation Of Fermionic Molecules Via Interisotope Feshbach Rmentioning

confidence: 99%

Formation of fermionic molecules via interisotope Feshbach resonances

2004

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“…Experimentally, the trapping and cooling of fermionic alkalis has been demonstrated reaching temperatures as low as ∼ T F /4 for 40 K [1] and 6 Li [2][3][4] with T F denoting the Fermi temperature. It is well known from condensed matter and nuclear physics that a gas composed of two different internal states of the same fermionic particle which interact via an attractive interaction is unstable to formation of so-called Cooper pairs, thus becoming a superfluid.…”

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Vortex state in superfluid trapped Fermi gases at zero temperature

Bruun

Viverit

2001

Phys. Rev. A

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We discuss various aspects of the vortex state of a dilute superfluid atomic Fermi gas at T = 0. The energy of the vortex in a trapped gas is calculated and we provide an expression for the thermodynamic critical rotation frequency of the trap for its formation. Furthermore, we propose a method to detect the presence of a vortex by calculating the effect of its associated velocity field on the collective mode spectrum of the gas.Inspired by the impressive progress in recent years in the field of Bose-Einstein condensation in dilute atomic gases, increasing attention is being devoted to examine the behavior of a gas of fermionic atoms at the same ultra-low temperatures. Experimentally, the trapping and cooling of fermionic alkalis has been demonstrated reaching temperatures as low as ∼ T F /4 for 40 K [1] and 6 Li [2-4] with T F denoting the Fermi temperature. It is well known from condensed matter and nuclear physics that a gas composed of two different internal states of the same fermionic particle which interact via an attractive interaction is unstable to formation of so-called Cooper pairs, thus becoming a superfluid. After the possibility of such superfluid transition for trapped Fermi gases was proposed [5], a lot of theoretical work has been focusing on various properties of this system [6]. At the same time a major experimental goal has become to observe the formation of the superfluid state.One of the intriguing properties of a superfluid is the possibility of forming quantized vortices. For a BoseEinstein condensate, the study of vortices has produced several interesting results [7]. Recently, some aspects of the vortex state of a trapped superfluid Fermi gas close to the critical temperature T c of the superfluid phase transition were considered [8]. In this paper we are interested in the properties of the vortex state of clouds of trapped Cooper-paired fermions at T = 0, and in particular in understanding under which conditions a vortex forms, what is its energy, and how it can be detected. We consider large systems where the coherence length ξ of the superfluid is much smaller than the extent of the cloud. In this limit, we are able to derive an analytical estimate of the energy of a vortex in a trap, thereby predicting the critical rotation frequency for its formation. Also, we propose a way of observing the vortex by calculating its effect on the collective mode spectrum of the gas. The paper is organized as follows: first in Sec. I, we examine for which values of the characteristic parameters the vortex is well localized within the gas. In Sec. II we present a simple model for calculating the energy of a vortex in a uniform superfluid Fermi system. Using the result of Sec. II, in Sec. III we calculate the energy of a singly quantized vortex in a trapped gas and from that we obtain the value of the thermodynamic critical rotation frequency for its formation. The problem of observing the vortex state is considered in Sec. IV, where we calculate how the presence of a vortex influences the collective...

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“…(iii) In QCD it occurs for different species of quarks (up, down, strange). If the mismatch is small and the two species are alternative states of the same particle (such as the spin up and down states of electrons or two hyperfinespin states of cold 40 K or 6 Li atoms as prepared in experiments [7,8,9, 10]), it can be favorable to equalize the Fermi surfaces, absorbing a cost in kinetic energy, and then to pair at zero momentum following BCS. For larger mismatches, LOFF-type ordering can occur.…”

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Interior Gap Superfluidity

2003

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We propose a new state of matter in which the pairing interactions carve out a gap within the interior of a large Fermi ball, while the exterior surface remains gapless. This defines a system which contains both a superfluid and a normal Fermi liquid simultaneously, with both gapped and gapless quasiparticle excitations. This state can be realized at weak coupling. We predict that a cold mixture of two species of fermionic atoms with different mass will exhibit this state. For electrons in appropriate solids, it would define a material that is simultaneously superconducting and metallic.Recent developments in ultracold alkali atomic gases [1] have revitalized interest in some basic qualitative questions of quantum many-body theory, because they promise to make a wide variety of conceptually interesting parameter regimes, which might previously have seemed academic or excessively special, experimentally accessible. With this motivation, and stimulated by questions in quantum chromodynamics (QCD) at high density [2, 3, 4], we here revisit the question of fermion pairing between species whose Fermi surfaces do not precisely match. We have found a possibility that seems to be new and certainly is interesting, and which could turn out to be relevant even for conventional solids.The standard Bardeen-Cooper-Schrieffer (BCS) [5] theory of superconductivity describes pairing between particles of equal and opposite momentum near a common Fermi surface. For classic s-wave superconductors the pairing occurs between electrons of opposite spin. In the presence of a weak magnetic field, and in particular in the case of ferromagnetic order, the Fermi surfaces of the opposite spins will not match, and the Cooper pairing instability, which was enhanced by vanishing energy denominators, will no longer occur at arbitrarily weak coupling. Larkin and Ovchinnikov and independently Fulde and Ferrell [6] showed that in this circumstance it might be favorable to effectively relatively translate the Fermi surfaces, pairing at a non-zero total momentum (LOFF phase).A simpler situation, conceptually, is that pairing occurs between two species whose Fermi surfaces do not match simply because their densities or effective masses differ. This possibility arises in several contexts. (i) In ultracold atom systems, it could occur simply because there are atoms of different elements. (ii) In solids it could occur for electron populations in two different bands. (iii) In QCD it occurs for different species of quarks (up, down, strange). If the mismatch is small and the two species are alternative states of the same particle (such as the spin up and down states of electrons or two hyperfinespin states of cold 40 K or 6 Li atoms as prepared in experiments [7,8,9, 10]), it can be favorable to equalize the Fermi surfaces, absorbing a cost in kinetic energy, and then to pair at zero momentum following BCS. For larger mismatches, LOFF-type ordering can occur. More elaborate forms of position-dependent ordering, with the superfluid gap having standing w...

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Stable, Strongly Attractive, Two-State Mixture of Lithium Fermions in an Optical Trap

Cited by 49 publications

References 17 publications

Formation of fermionic molecules via interisotope Feshbach resonances

Formation of fermionic molecules via interisotope Feshbach resonances

Vortex state in superfluid trapped Fermi gases at zero temperature

Interior Gap Superfluidity

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