Experimental realization of a long-range antiferromagnet in the Hubbard model with ultracold atoms

TL;DR

This study demonstrates the experimental realization of a long-range antiferromagnet in a 2D Hubbard model using ultracold atoms, providing insights into strongly correlated electron systems and the doped regime relevant to high-temperature superconductivity.

Contribution

First experimental observation of antiferromagnetic long-range order in a 2D Hubbard model with ultracold fermions using site-resolved imaging.

Findings

Detected antiferromagnetic long-range order via spin structure factor peak.

Observed persistent antiferromagnetic order up to 15% hole doping.

Achieved low temperature T/t = 0.25(2) in the experiment.

Abstract

Many exotic phenomena in strongly correlated electron systems emerge from the interplay between spin and motional degrees of freedom. For example, doping an antiferromagnet gives rise to interesting phases including pseudogap states and high-temperature superconductors. A promising route towards achieving a complete understanding of these materials begins with analytic and computational analysis of simplified models. Quantum simulation has recently emerged as a complementary approach towards understanding these models. Ultracold fermions in optical lattices offer the potential to answer open questions on the low-temperature regime of the doped Hubbard model, which is thought to capture essential aspects of the cuprate superconductor phase diagram but is numerically intractable in that parameter regime. A new perspective is afforded by quantum gas microscopy of fermions, which allows readout of magnetic correlations at the site-resolved level. Here we report the realization of an antiferromagnet in a repulsively interacting Fermi gas on a 2D square lattice of approximately 80 sites. Using site-resolved imaging, we detect (finite-size) antiferromagnetic long-range order (LRO) through the development of a peak in the spin structure factor and the divergence of the correlation length that reaches the size of the system. At our lowest temperature of T/t = 0.25(2) we find strong order across the entire sample. Our experimental platform enables doping away from half filling, where pseudogap states and stripe ordering are expected, but theoretical methods become numerically intractable. In this regime we find that the antiferromagnetic LRO persists to hole dopings of about 15%, providing a guideline for computational methods. Our results demonstrate that quantum gas microscopy of ultracold fermions in optical lattices can now address open questions on the low-temperature Hubbard model.