Experimental realization of Qi-Wu-Zhang model with spin-orbit-coupled ultracold fermions

Ultracold atoms can be used for simulating various physical systems. As one of the fundamental models for the quantum anomalous Hall (QAH) effect, the Qi-Wu-Zhang model has broad impact on condensed matter research and becomes a building block for many other models. Alkaline-earth atoms, with the featured two-electron outer shell structure, possess additional advantages for realizing spin-orbit-coupled systems and the Qi-Wu-Zhang model. Based on the optical Raman lattice technique, we report experimental realization of the Qi-Wu-Zhang model for the QAH phase in ultracold Sr-87 fermions with two-dimensional (2D) spin-orbit (SO) coupling. We develop an experimental protocol of pump-probe quench measurement to probe, with minimal heating, the resonant spin flipping on particular quasi-momentum subspaces called band-inversion surfaces. With this protocol we demonstrate Dirac-type 2D SO coupling in a fermionic system and detect nontrivial band topology by observing the change of band-inversion surfaces as the two-photon detuning is tuned. Furthermore, we slowly load atoms into optical Raman lattices and observe the non-trivial band topology by measuring the spin textures.