When does a Fermi puddle become a Fermi sea? Emergence of pairing in two-dimensional trapped mesoscopic Fermi gases

Abstract

Pairing lies at the heart of superfluidity in fermionic systems. Motivated by recent experiments in mesoscopic Fermi gases, we study up to six fermionic atoms with equal masses and equal populations in two different spin states, confined in a quasi-two-dimensional harmonic trap. We couple a stochastic variational approach with the use of an explicitly correlated Gaussian basis set, which enables us to obtain highly accurate energies and structural properties. Utilising two-dimensional two-body scattering theory with a finite-range Gaussian interaction potential, we tune the effective range to model realistic quasi-two-dimensional scattering. We calculate the excitation spectrum, pair correlation function, and number of pairs as a function of increasing attractive interaction strength. For up to six fermions in the ground state, we find that opposite spin and momentum pairing is maximised well below the Fermi surface in momentum space. By contrast, corresponding experiments on twelve fermions have found that pairing is maximal at the Fermi surface and strongly suppressed beneath [M. Holten et al., Nature 606, 287-291 (2022)]. This suggests that the Fermi sea $-$ which acts to suppress pairing at low momenta via Pauli blocking $-$ emerges in the transition from six to twelve particles.

38 pages, 7 figures; accepted version

References in corpus (16)

• Many-Body Physics with Ultracold Gases
• Theory of ultracold Fermi gases
• Vortices and Superfluidity in a Strongly Interacting Fermi Gas
• Molecular Probe of Pairing in the BEC-BCS Crossover
• Energetics and Structural Properties of Trapped Two-Component Fermi Gases
• Spectrum and Dynamics of the BCS-BEC crossover from a few-body perspective
• Berezinskii-Kosterlitz-Thouless transition in trapped quasi-two-dimensional Fermi gas near a Feshbach resonance
• Bound states in a quasi-two-dimensional Fermi gas
• Condensate Fraction of a Two-Dimensional Attractive Fermi Gas
• BCS-BEC Crossover of a Quasi-two-dimensional Fermi Gas: the Significance of Dressed Molecules
• Universality of the unitary Fermi gas: A few-body perspective
• A long-lived Higgs mode in a two-dimensional confined Fermi gas
• Trapped unitary two-component Fermi gases with up to ten particles
• Cold Fermionic Atoms in Two-Dimensional Traps -- Pairing versus Hund's Rule
• Coupled pair approach for strongly-interacting trapped fermionic atoms
• Few-to-many-particle crossover of pair excitations in a superfluid

Cited by in corpus (1)

• Impurity immersed in a two-component few-fermion mixture in a one-dimensional harmonic trap