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arXiv:2610.26997

Achieving ultrahigh-temperature superfluidity in atomic Fermi gases by suppressing pairing fluctuations

Lin Sun, Qijin Chen

Published Oct 19, 2026• 0 citations
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Abstract

Achieving room-temperature superconductivity has been a long-sought goal of both the physics community and the industry. The superfluid transition temperature $T_\mathrm{c}$ of a Fermi system initially increases with increasing pairing strength between fermions following the mean-field prediction of the Bardeen-Cooper-Schrieffer (BCS) theory, and is then suppressed by pairing fluctuations as the strength increases further, which prevents $T_\mathrm{c}$ from becoming high. Here we propose a mechanism for suppressing pairing fluctuations using the synergy between population imbalance and momentum space confinement in lattice systems, enabling an ultrahigh $T_\mathrm{c}$ at moderately strong attraction. We show that in a three-dimensional optical lattice, strong Pauli exclusion between paired and excess majority fermions pushes up the pair excitation energy and suppresses finite-momentum pairing fluctuations. The mechanism is general to any lattice with a finite Brillouin zone; the optimal imbalance is modest ($p\lesssim 0.1$), keeping the Zeeman field small and avoiding orbital complications. The gapped pair dispersion at moderate imbalance exponentially suppresses thermal condensate depletion, providing a testable signature. The gapped dispersion, enhanced condensate fraction, and pseudogap reduction are all accessible in present-day experiments. This work opens new avenues toward room-temperature superconductivity.

DOI
10.48550/arxiv.2610.26997

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We study the ground-state phase diagram of population balanced and imbalanced ultracold atomic Fermi gases with a short-range attractive interaction throughout the crossover from BCS to Bose-Einstein condensation (BEC), in a two-dimensional (2D) optical lattice comprised of a 2D array of 1D lines. We find that the mixing of lattice and continuum dimensions, together with population imbalance, has an extraordinary effect on pairing and the superfluidity of atomic Fermi gases. In the balanced case, the superfluid ground state prevails over the majority of the phase space. However, for relatively small lattice hopping integral ttt and large lattice constant ddd, a pair density wave (PDW) emerges unexpectedly at intermediate coupling strength, and the nature of the in-plane and overall pairing changes from particlelike to holelike in the BCS and unitary regimes, associated with an abnormal increase in the Fermi volume with the pairing strength. In the imbalanced case, the stable polarized superfluid phase shrinks to only a small portion of the entire phase space spanned by t,dt, dt,d, imbalance ppp, and interaction strength UUU, mainly in the bosonic regime of low ppp, moderately strong pairing, relatively large ttt, and small ddd. Due to the Pauli exclusion between paired and excessive fermions within the confined momentum space, a PDW phase emerges and the overall pairing evolves from particlelike into holelike, as the pairing strength grows stronger in the BEC regime. In both cases, the ground-state property is largely governed by the Fermi surface topology. These findings are very different from the cases of a pure 3D continuum, a 3D lattice, or a 1D optical lattice.
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