Observation of canted antiferromagnetism with ultracold fermions in an optical lattice

TL;DR

This study uses ultracold fermions in optical lattices to observe canted antiferromagnetism and spin correlations, providing insights into magnetic responses relevant to high-temperature superconductivity in cuprates.

Contribution

First site-resolved measurements of the Fermi-Hubbard model with spin imbalance revealing canted antiferromagnetism and anisotropic spin correlations, advancing quantum simulation of strongly correlated materials.

Findings

Observation of short-range canted antiferromagnetism at half-filling.

Detection of increased rotational anisotropy of spin correlators with polarization.

Non-monotonic doping dependence of polarization resembling cuprate behavior.

Abstract

Understanding the magnetic response of the normal state of the cuprates is considered a key piece in solving the puzzle of their high-temperature superconductivity. The essential physics of these materials is believed to be captured by the Fermi-Hubbard model, a minimal model that has been realized with cold atoms in optical lattices. Here we report on site-resolved measurements of the Fermi-Hubbard model in a spin-imbalanced atomic gas, allowing us to explore the response of the system to large effective magnetic fields. We observe short-range canted antiferromagnetism at half-filling with stronger spin correlations in the direction orthogonal to the magnetization, in contrast with the spin-balanced case where identical correlations are measured for any projection of the pseudospin. The rotational anisotropy of the spin correlators is found to increase with polarization and with distance between the spins. Away from half-filling, the polarization of the gas exhibits non-monotonic behavior with doping for strong interactions, resembling the behavior of the magnetic susceptibility in the cuprates. We compare our measurements to predictions from Determinantal Quantum Monte Carlo (DQMC) and Numerical Linked Cluster Expansion (NLCE) algorithms and find good agreement. Calculations on the doped system are near the limits of these techniques, illustrating the value of cold atom quantum simulations for studying strongly-correlated materials.