Observation of 2D fermionic Mott insulators of $^{40}$K with single-site resolution

TL;DR

This study uses ultracold fermionic atoms in an optical lattice to directly observe and characterize different quantum states of the 2D Fermi-Hubbard model with single-site resolution, revealing local magnetic properties.

Contribution

First direct site-resolved observation of characteristic states in the 2D fermionic Hubbard model with ultracold atoms, including measurements of local moments and magnetic correlations.

Findings

Realized metallic, Mott-insulating, and band-insulating states.

Measured local moments as a function of temperature and chemical potential.

Achieved low entropy per particle, enabling detection of antiferromagnetic correlations.

Abstract

We report on the site-resolved observation of characteristic states of the two-dimensional repulsive Fermi-Hubbard model, using ultracold $^{40}$K atoms in an optical lattice. By varying the tunneling, interaction strength, and external confinement, we realize metallic, Mott-insulating, and band-insulating states. We directly measure the local moment, which quantifies the degree of on-site magnetization, as a function of temperature and chemical potential. Entropies per particle as low as $0.99(6)\,k_B$ indicate that nearest-neighbor antiferromagnetic correlations should be detectable using spin-sensitive imaging.