Emergent Bose-Fermi mixture from a spin-imbalanced Hubbard gas

The attractive Fermi-Hubbard model with spin and charge doping is predicted to host a variety of exotic phases, such as FFLO pairing and d-wave antiferromagnetism. In this work, by employing a quantum gas microscope, the microscopic behavior of fermion pairs at finite magnetization is explored at various densities and magnetizations. We first demonstrate the robustness of fermion pairing against spin-imbalance by observing the strongly suppressed spin fluctuations. By measuring the excess density around minority atoms, we are able to observe a crossover from on-site doublons to extended pairing with decreasing interaction strength. With higher magnetization, the Pauli hole is observed between excess spins via singlon-singlon correlations, indicating the emergence of a degenerate Fermi surface. We further reveal the repulsive nature between the bosonic pairs and excess fermions by measuring their density correlation, confirming that the system can be effectively described as a hard-core Bose-Fermi mixture. Finally, by using local correlations, we are able to characterize the spin-imbalanced Fermi-Hubbard gas via different categories at various densities and magnetizations, based on the presence or absence of many-body ordering and Pauli repulsion.