Hole Pairing, Density Structure Formation and Pseudogap in the Doped 2D Fermi Hubbard Model

Quantum simulation using ultracold atoms and molecules has opened a new research field to probe quantum matter in- and out-of-equilibrium. In fermionic quantum matter, mixed two-dimensional systems can substantially boost the pairing energy of holes and have enabled us to observe hole pairing in 2d and extended density structures that can be viewed as precursors of stripe phases in doped systems. Furthermore, we probe higher order spin correlations around mobile dopants, finding dominant 4th and 5th order correlations that provide direct proof of spin strings attached to the holes. We also evaluate spin fluctuations for doped and undoped system and compare these to advances numerical methods such as QMC and METTS, showing that ultracold quantum simulators are entering the pseudogap regime. Evaluation of higher order correlators in this regime can shed new light on fundamental properties of the pseudogap.