Cold asymmetrical fermion superfluids (original) (raw)
Related papers
Phase Separation in Asymmetrical Fermion Superfluids
Physical Review Letters, 2003
Motivated by recent developments on cold atom traps and high density QCD we consider fermionic systems composed of two particle species with different densities. We argue that a mixed phase composed of normal and superfluid components is the energetically favored ground state. We suggest how this phase separation can be used as a probe of fermion superfluidity in atomic traps.
Phase Transition in Unbalanced Fermion Superfluids
2006
In this chapter the recent theoretical work on phase transition in imbalanced fermion superfluids is reviewed. The imbalanced systems are those in which the two fermionic species candidate to form pairing have different Fermi surfaces or densities. We consider systems subjected to weak interactions. In this scenario two distinct phase transitions are predicted to occur. A thermodynamical phase transition, induced by the temperature (T), and a quantum phase transition as a function of the increasing chemical potentials asymmetry, that takes place at zero temperature. We also briefly discuss some recent experimental work at non-zero T with imbalanced Fermi gases in cold atomic traps.
Interior gap superfluidity in a two-component Fermi gas of atoms
Physical Review A, 2004
A new superfluid phase in Fermi matter, termed as "interior gap" (IG) or "breached pair", has been recently predicted by Liu and Wilczek [Phys.Rev.Lett. 90, 047002 (2003)]. This results from pairing between fermions of two species having essentially different Fermi surfaces. Using a nonperturbative variational approach, we analyze the features, such as energy gap, momentum distributions, and elementary excitations associated with the predicted phase. We discuss possible realization of this phase in two-component Fermi gases in an optical trap.
Anisotropic superfluidity in the two-species polar Fermi gas
2010
We study the superfluid pairing in a two-species gas of heteronuclear fermionic molecules with equal density. The interplay of the isotropic s-wave interaction and anisotropic long-range dipolar interaction reveals rich physics. We find that the single-particle momentum distribution has a characteristic ellipsoidal shape that can be reasonably represented by a deformation parameter α defined similarly to the normal phase. Interesting momentum-dependent features of the order parameter are identified. We calculate the critical temperatures of both the singlet and triplet superfluid, suggesting a possible pairing symmetry transition by tuning the s-wave or dipolar interaction strength.
Induced superfluidity of imbalanced Fermi gases near unitarity
Physical Review A, 2012
The induced intraspecies interactions among the majority species, mediated by the minority species, is computed for a population-imbalanced two-component Fermi gas. Although the Feshbachresonance mediated interspecies interaction is dominant for equal populations, leading to singlet s-wave pairing, we find that in the strongly imbalanced regime the induced intraspecies interaction leads to p-wave pairing and superfluidity of the majority species. Thus, we predict that the observed spin-polaron Fermi liquid state in this regime is unstable to p-wave superfluidity, in accordance with the results of Kohn and Luttinger, below a temperature that, near unitarity, we find to be within current experimental capabilities. Possible experimental signatures of the p-wave state using radiofrequency spectroscopy as well as density-density correlations after free expansion are presented.
Physical Review A, 2010
By applying the recently proposed antisymmetric superfluid local density approximation (ASLDA) to strongly interacting polarized atomic gases at unitarity in very elongated traps, we find families of Larkin-Ovchinnikov (LO) type of solutions with prominent transversal oscillation of pairing potential. These LO states coexist with a superfluid state having a smooth pairing potential. We suggest that the LO phase could be accessible experimentally by increasing adiabatically the trap aspect ratio. We show that the local asymmetry effects contained in ASLDA do not support a deformed superfluid core predicted by previous Bogoliubov-de Gennes treatments.
Superfluidity in Two-Dimensional Imbalanced Fermi Gases
2011
We study the zero temperature ground state of a two-dimensional atomic Fermi gas with chemical potential and population imbalance in the mean-field approximation. All calculations are performed in terms of the two-body binding energy epsilonB\epsilon_BepsilonB, whose variation allows to investigate the evolution from the BEC to the BCS regimes. By means of analytical and exact expressions we show that, similarly to what is found in three dimensions, at fixed chemical potentials, BCS is the ground state until the critical imbalance hch_chc after which there is a first-order phase transition to the normal state. We find that hch_chc, the Chandrasekhar-Clogston limit of superfluidity, has the same value as in three dimensional systems. We show that for a fixed ratio epsilonB/epsilonF\epsilon_B/\epsilon_FepsilonB/epsilonF, where epsilonF\epsilon_FepsilonF is the two-dimensional Fermi energy, as the density imbalance mmm is increased from zero, the ground state evolves from BCS to phase separation to the normal state. At the critical imbalance mcm_cmc phase separation is not supported and the normal phase is energetically preferable. The BCS-BEC crossover is discussed in balanced and imbalanced configurations. Possible pictures of what may be found experimentally in these systems are also shown. We also investigate the necessary conditions for the existence of bound states in the balanced and imbalanced normal phase.
Resonance Superfluidity in a Quantum Degenerate Fermi Gas
Physical Review Letters, 2001
We consider the superfluid phase transition that arises when a Feshbach resonance pairing occurs in a dilute Fermi gas. We apply our theory to consider a specific resonance in potassium ( 40 K), and find that for achievable experimental conditions, the transition to a superfluid phase is possible at the high critical temperature of about 0.5 TF . Observation of superfluidity in this regime would provide the opportunity to experimentally study the crossover from the superfluid phase of weakly-coupled fermions to the Bose-Einstein condensation of strongly-bound composite bosons.