  We study the far-from-equilibrium dynamics of isolated two-dimensional
Heisenberg antiferromagnets. We consider spin spiral initial conditions which
imprint a position-dependent staggered-magnetization (or Neel order) in the
two-dimensional lattice. Remarkably, we find a long-lived prethermal regime
characterized by self-similar behavior of staggered magnetization fluctuations,
although the system has no long-range order at finite energy and the staggered
magnetization does not couple with conserved charges. Exploiting the separation
of length scales introduced by the initial condition, we derive a simplified
analytical model that allow us to compute the spatial-temporal scaling
exponents and power-law distribution of the staggered magnetization
fluctuations analytically, and find excellent agreement with numerical
simulations using phase space methods. The scaling exponents are insensitive to
details of the initial condition, in particular, no fine-tuning of energy is
required to trigger the self-similar scaling regime. Compared with recent
results on far-from-equilibrium universality on the Heisenberg ferromagnet, we
find quantitatively distinct spatial-temporal scaling exponents, therefore
suggesting that the same model with ferromagnetic and antiferromagnetic initial
conditions can host different universal regimes. Our predictions are relevant
to ultra-cold atoms simulators of Heisenberg magnets and driven
antiferromagnetic insulators.
