Pairing correlations across the superfluid phase transition in the unitary Fermi gas

Abstract

In the two-component Fermi gas with a contact interaction, a pseudogap regime can exist at temperatures between the superfluid critical temperature $T_c$ and a temperature $T^{\ast }>T_c$. This regime is characterized by pairing correlations without superfluidity. However, in the unitary limit of infinite scattering length, the existence of this regime is still debated. To help address this, we have applied finite-temperature auxiliary-field quantum Monte Carlo (AFMC) to study the thermodynamics of the superfluid phase transition and signatures of the pseudogap in the spin-balanced homogeneous unitary Fermi gas. We present results at finite filling factor $\nu \simeq 0.06$ for the condensate fraction, an energy-staggering pairing gap, the spin susceptibility, and the heat capacity, and compare them to experimental data when available. In contrast to previous AFMC simulations, our model space consists of the complete first Brillouin zone of the lattice, and our calculations are performed in the canonical ensemble of fixed particle number. The canonical ensemble AFMC framework enables the calculation of a model-independent gap, providing direct information on pairing correlations without the need for numerical analytic continuation. We use finite-size scaling to estimate $T_c$ at the corresponding filling factor. We find that the energy-staggering pairing gap vanishes above $T_c$, showing no pseudogap effects, and that the spin susceptibility shows a substantially reduced signature of a spin gap compared to previously reported AFMC simulations.

5 pages, 2 figures, and 6 pages, 9 figures of supplemental material

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• Pairing and the spin susceptibility of the polarized unitary Fermi gas in the normal phase
• Mesoscopic spin transport between strongly interacting Fermi gases
• Eliminating the wave function singularity for ultracold atoms by similarity transformation
• Dissipative Dynamics of Quantum Vortices in Fermionic Superfluid
• Unitary $p$-wave Fermi gas in one dimension
• Superfluid Condensate Fraction and Pairing Wave Function of the Unitary Fermi Gas
• Second sound with ultracold atoms: A brief historical account
• Structure Factors of The Unitary Gas Under Supernova Conditions
• A Stable, Recursive Auxiliary Field Quantum Monte Carlo Algorithm in the Canonical Ensemble: Applications to Thermometry and the Hubbard Model
• From odd-even staggering to the pairing gap in neutron matter
• BCS-BEC Crossover Effects and Pseudogap in Neutron Matter
• Spatial emergence of Off-Diagonal Long-Range Order throughout the BCS-BEC crossover
• Low-Dimensional Fluctuations and Pseudogap in Gaudin-Yang Fermi Gases
• Quantum Many-Body Calculations using Body-Centered Cubic Lattices
• Three-body contact for fermions. I. General relations
• The normal state of attractive Fermi gases from coupled-cluster theory
• A lattice pairing-field approach to ultracold Fermi gases
• Precision thermodynamics of the strongly interacting Fermi gas in two dimensions
• Ab initio study of the neutron and Fermi polarons on the lattice