  We study the impact of cooperative many-body effects on the operation of
periodically-driven quantum thermal machines, particularly heat engines and
refrigerators. In suitable geometries, $N$ two-level atoms can exchange energy
with the driving field and the (hot and cold) thermal baths at a faster rate
than a single atom due to their SU(2) symmetry that causes the atoms to behave
as a collective spin-$N/2$ particle. This cooperative effect boosts the power
output of heat engines compared to the power output of $N$ independent,
incoherent, heat engines. In the refrigeration regime, similar cooling-power
boost takes place.
