Observation of Effective Attractive Interactions in a cold atom bilayer Fermi-Hubbard System

With the discovery of the nickelate high-Tc superconductors, bilayer t-J models have gained attention as a potential framework to explain the properties of these materials [1-3]. Bilayer t-J models can be considered a special case of a more general bilayer Fermi-Hubbard model formed by extending the 2D Fermi-Hubbard model with the addition of a second copy of the system coupled by an independent tunneling. The two layers may also have a relative detuning, suppressing interlayer tunneling and allowing only superexchange. Our quantum gas microscope---designed for studying a 2D Fermi-Hubbard system using 40K atoms in an optical lattice---can readily be upgraded to explore bilayer Hubbard systems utilizing the existing bilayer imaging apparatus [4]. In our bilayer Hubbard system, we observe an effective attractive interaction between fermions in the different layers despite on-site repulsive interactions. We systematically study this interaction over a range of interlayer tunneling couplings, interlayer detunings, and on-site interaction strengths. These results may provide a path towards exploring superfluidity in repulsive Hubbard systems.

[1] Sun, Hualei, et al. "Signatures of superconductivity near 80K in a nickelate under high pressure." Nature 621.7979 (2023): 493-498.

[2] Luo, Zhihui, et al. "Bilayer two-orbital model of La3Ni2O7 under pressure." Physical review letters 131.12 (2023): 126001.

[3] Qu, Xing-Zhou, et al. "Bilayer t-J-J⊥ model and magnetically mediated pairing in the pressurized nickelate La3Ni2O7." Physical Review Letters 132.3 (2024): 036502.

[4] Hartke, Thomas, et al. "Doublon-hole correlations and fluctuation thermometry in a Fermi-Hubbard gas." Physical review letters 125.11 (2020): 113601.