Homogeneous Fermionic Hubbard Gases in a Flattop Optical Lattice

Fermionic atoms in a large-scale, homogeneous optical lattice provide an ideal quantum simulator for investigating the fermionic Hubbard model, yet achieving this remains challenging. Here, by developing a hybrid potential that integrates a flat-top optical lattice with an optical box trap, we successfully realize the creation of three-dimensional, homogeneous fermionic Hubbard gases across approximately 8×10^{5} lattice sites. This homogeneous system enables us to capture a well-defined energy band occupation that aligns perfectly with the theoretical calculations for a zero-temperature, ideal fermionic Hubbard model. Furthermore, by employing novel radio-frequency spectroscopy, we precisely measure the doublon fraction D as a function of interaction strength U and temperature T, respectively. The crossover from metal to Mott insulator is detected, where D smoothly decreases with increasing U. More importantly, we observe a nonmonotonic temperature dependence in D, revealing the Pomeranchuk effect and the development of extended antiferromagnetic correlations.