  Emulation of gauge fields for ultracold atoms provides access to a class of
exotic states arising in strong magnetic fields. Here we report on the
experimental realisation of tunable staggered gauge fields in a periodically
driven triangular lattice. For maximal staggered magnetic fluxes, the doubly
degenerate superfluid ground state breaks both a discrete Z2 (Ising) symmetry
and a continuous U(1) symmetry. By measuring an Ising order parameter, we
observe a thermally driven phase transition from an ordered antiferromagnetic
to an unordered paramagnetic state and textbook-like magnetisation curves. Both
the experimental and theoretical analysis of the coherence properties of the
ultracold gas demonstrate the strong influence of the Z2 symmetry onto the
condensed phase.
