Doping a frustrated Fermi-Hubbard magnet

The Fermi-Hubbard model on the anisotropic triangular lattice is a fundamental setting for studying the effects of geometric frustration on strongly correlated fermions, which is believed to generate intriguing magnetic phases such as quantum spin liquids. The model’s phase diagram, however, remains debated even at half-filling, and is still more unclear in the presence of doping. Here we use a quantum gas microscope to probe the local spin order of the anisotropic triangular Fermi-Hubbard model as a function of anisotropy and doping. In Mott insulating samples, we observe how frustration weakens magnetic correlations and drives a transition from a collinear Néel antiferromagnet to a short-range 120^· spiral phase. Upon doping, magnetic correlations show a pronounced particle-hole asymmetry and suggest a transition to ferromagnetism at heavy particle doping. This work opens the door for future studies of possible chiral or superconducting phases in triangular lattices, and paves the way towards realizing non-bipartite square lattice Hubbard models that may be crucial in modeling the superconducting cuprates.