Hannover 2013 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 59: Quantum gases: Optical lattices III

Q 59.4: Talk

Friday, March 22, 2013, 11:45–12:00, F 342

Observation of Ising symmetry breaking in a triangular optical lattice — •Christoph Ölschläger¹, Julian Struck¹, Malte Weinberg¹, Juliette Simonet¹, Robert Höppner¹, Ludwig Mathey¹, Philipp Hauke², Maciej Lewenstein², André Eckardt³, Patrick Windpassinger¹, and Klaus Sengstock¹ — ¹Institut für Laserphysik, Universität Hamburg, Germany — ²ICFO - Institut de Ciències Fotòniques, Castelldefels, Spain — ³MPI für Physik komplexer Systeme, Dresden, Germany

Ultracold quantum gases in optical lattices are well suited to investigate and simulate systems connected to solid state physics. Here we report on the experimental realization of ultracold atoms in a triangular lattice with an emergent discrete Ising (Z2) and continuous (U(1)) symmetry by engineering fully tunable artificial staggered gauge fields via lattice shaking. For staggered pi-fluxes the ground state is twofold degenerate and we observe a thermally driven phase transition between an unordered (paramagnetic-like) state and an ordered (ferromagnetic-like) state, where the system shows a spontaneous magnetization. Via the full control over the flux strength, it is in addition possible to lift the degeneracy on purpose, e.g. to break the Ising symmetry, and thus measure the magnetization depending on the field and temperature. This can be viewed as in close analogy to a classical Ising-spin model in an external homogeneous magnetic field showing characteristic magnetization dependences below and above a critical temperature. We acknowledge support from the Deutsche Forschungsgemeinschaft within SFB925 and FOR801.