Abstract
The metastability associated with the first-order transition from the normal to the superfluid phase is investigated in the phase diagram of two-component polarized Fermi gases. We begin by detailing the dominant decay processes of single quasiparticles, determining the momentum thresholds of each process and calculating their rates. This understanding is then applied to a Fermi sea of polarons, and we predict a region of metastability for the normal partially polarized phase. We propose experiments to observe the threshold of the metastable region, the interaction strength at which the quasiparticle ground state changes character, and the decay rate of polarons.
Highlights
BackgroundOur starting point is an understanding of the single quasiparticle ground state as a function of 1/kF↑a going from unitarity (1/kF↑a → 0) to the ‘Bose–Einstein condensate (BEC)’ limit (1/kF↑a → +∞) (see figure 1)
We propose the use of a Fermi sea of polarons as an experimental probe for determining the momentum threshold of the quasiparticle decay
Our starting point is an understanding of the single quasiparticle ground state as a function of 1/kF↑a going from unitarity (1/kF↑a → 0) to the ‘Bose–Einstein condensate (BEC)’ limit (1/kF↑a → +∞)
Summary
Our starting point is an understanding of the single quasiparticle ground state as a function of 1/kF↑a going from unitarity (1/kF↑a → 0) to the ‘Bose–Einstein condensate (BEC)’ limit (1/kF↑a → +∞) (see figure 1). At the critical value 1/kF↑(a)c ∼ 0.88, the zero-momentum energies of the polaron and the molecule cross. In figure 1 and throughout this paper, we use the polaron energy calculated using the wave function proposed by Chevy [14]. These masses and energies for both polarons and molecules have been found to be very accurate in comparison with quantum Monte Carlo calculations [11, 19]. Molecule and polaron zero momentum energies as a function of interaction strength on the ‘BEC’ side. The dot-dashed line marks the critical interaction strength 1/(kF↑a)c ∼ 0.88. To the left of it, the polaron energy is lower, and to the right it is the molecule that becomes the ground state
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