# Mainz 2017 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 46: Quantum Gases: Fermions I

### Q 46.1: Gruppenbericht

### Donnerstag, 9. März 2017, 11:00–11:30, P 204

**Observation of antiferromagnetic long-range order in the Hubbard model with ultracold atoms** — •Daniel Greif, Anton Mazurenko, Christie S. Chiu, Geoffrey Ji, Maxwell F. Parsons, Fabian Grusdt, Richard Schmidt, Marton Kanasz-Nagy, Eugene Demler, and Markus Greiner — Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA

Quantum gas microscopy of ultracold fermionic atoms in optical lattices opens new perspectives for addressing long-standing open questions on strongly correlated low-temperature phases in the Hubbard model. For example, the precise character of the phases emerging when doping an antiferromagnet away from half-filling is still not well understood. We report on the observation of antiferromagnetic long-range order in a repulsively interacting Fermi gas of Li-6 atoms on a 2D square lattice of approximately 80 sites at temperatures *T*/*t*=0.25. Using single-site resolution, the ordered state is directly detected from a peak in the spin structure factor and a diverging correlation length of the spin correlation function. In the long-range ordered state we measure staggered magnetizations exceeding 50% of the ground-state value. When doping away from half-filling into a numerically intractable regime, we find that long-range order extends to doping concentrations of about 15%. Our results pave the way for directly addressing open questions on pseudo-gap states and high-temperature superconductivity.