Fig. 4: Example of spin configurations during a period-2 limit cycle at zero temperature.

Spin configurations a and c are for the same angle ϕ of the driving field, but the spin configuration is different the second time through the driving cycle. Likewise, spin configurations b and d are for the same angle ϕ of the driving field, but the spin configuration is different the second time through the driving cycle. For this particular disorder configuration and system size, the spin configurations repeat every 2 periods of the driving cycle. Here the driving field strength is H = 0.04J, and the system size is 160 × 160. See Fig. 1 of Supplementary Information and videos22 of simulation results for further examples.