Heidelberg 2015 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 11: Quantum Gases: Fermions II

Q 11.6: Talk

Monday, March 23, 2015, 16:00–16:15, K/HS2

Exploring topology with optical lattices: The Haldane model and beyond — •Gregor Jotzu, Michael Messer, Rémi Desbuquois, Martin Lebrat, Thomas Uehlinger, Frederik Görg, Daniel Greif, and Tilman Esslinger — Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland

The Haldane model on the honeycomb lattice is a paradigmatic example of a Hamiltonian featuring topologically distinct phases of matter and describes a mechanism through which a quantum Hall effect can appear as an intrinsic property of a band-structure. We report on the experimental realisation of the Haldane model using ultracold fermionic atoms. The model is based on breaking time-reversal symmetry, which is achieved through the introduction of complex next-nearest-neighbour tunnelling terms, which we induce through circular modulation of the lattice position. Addtionally, we create an energy offset between neighbouring sites to break inversion symmetry. Breaking either of these symmetries opens a gap in the band-structure, which is probed using momentum-resolved interband transitions. We explore the resulting Berry-curvatures by applying a constant force to the atoms and find orthogonal drifts analogous to a Hall current. The competition between both broken symmetries gives rise to a transition between topologically distinct regimes. By identifying the vanishing gap at a single Dirac point, we map out this transition line experimentally and compare it to calculations using Floquet theory. Our approach is suitable even for interacting fermionic systems and can be extendet to create spin-dependent and spatially varying Hamiltonians.