13 September 2013
Ultracold atoms on a triangular optical lattice

Laser beams generated triangular lattice in which different kind of magnetic (spin) order can be realized.

Engineering Ising-XY spin-models in a triangular lattice using tunable artificial gauge fields in

*Nature Physics*Spontaneous symmetry breaking is a key element in the description and characterization of phase transitions in many areas of science and technology: from statistical physics to metallurgy. Driven by thermal or quantum fluctuations, at a transition to an ordered phase, the respective low-energy state breaks some of its basic symmetries, such as rotational, translation symmetry etc. The presence and interplay of different symmetries naturally raises the question of a coupling between order parameters, which may give rise to new classes of phase transitions. Research groups led by ICREA Professor at ICFO, Maciej Lewenstein, in collaboration with the Hamburg group led by Klaus Sengstock, report in*Nature Physics*on the utilization of ultracold atoms on a triangular optical lattice to create a system with combined rotational symmetry (like the symmetry of positions of a compass neddle and discrete, so called Ising symmetry (changing magnetization by a factor plus/minus one). The latter is generated by an artificial magnetic field, in analogy to a transversal homogeneous magnetic field in the Ising-spin model. A thermally driven “textbook like” Ising-type phase transition from an ordered, ferromagnetic to an unordered was observed, and the resulting hysteresis was measured.