Antiferromagnetic correlations in two-dimensional fermionic Mott-insulating and metallic phases

TL;DR

This study investigates how antiferromagnetic correlations develop in two-dimensional ultracold fermionic gases, revealing their dependence on temperature, doping, and interaction strength, and connecting these findings to models of quantum magnetism.

Contribution

It provides experimental measurements of antiferromagnetic correlations in 2D fermionic systems, demonstrating the transition from Hubbard to Heisenberg behavior and the effects of doping.

Findings

Antiferromagnetic correlations increase as temperature decreases near half-filling.

Doping suppresses magnetic correlations, indicating their sensitivity to carrier concentration.

Data aligns with the Heisenberg model at strong interactions and half-filling.

Abstract

Near zero temperature, quantum magnetism can non-trivially arise from short-range interactions, but the occurrence of magnetic order depends crucially on the interplay of interactions, lattice geometry, dimensionality and doping. Even though the consequences of this interplay are not yet fully understood, quantum magnetism is believed to be connected to a range of complex phenomena in the solid state, for example, in the context of high-$T_c$ superconductivity and spin liquids in frustrated lattices. Ultracold atomic Fermi gases in optical lattices constitute an experimental system with unrivalled tunability and detection capabilities to explore quantum magnetism by analog quantum simulation. In this work, we study the emergence of antiferromagnetic correlations between ultracold fermionic atoms in two dimensions with decreasing temperature. We determine the magnetic susceptibility of the Hubbard model from simultaneous measurements of the in-situ density of both spin components. At half-filling and strong interactions our data approach the Heisenberg model of localized spins with antiferromagnetic correlations. Moreover, we observe the disappearance of magnetic correlations when the system is doped away from half-filling. Our observation of the dependence of quantum magnetism on doping paves the way for future studies on the emergence of pseudogap and pairing phenomena away from half-filling.