  We investigate numerically and experimentally the near-field response of
disordered arrays comprising asymmetrically split ring resonators that exhibit
strong cooperative response. Our simulations treat the unit cell split ring
resonators as discrete pointlike oscillators with associated electric and
magnetic point dipole radiation, while the strong cooperative radiative
coupling between the different split rings is fully included at all orders. The
methods allow to calculate local field and Purcell factor enhancement arising
from the collective electric and magnetic excitations. We find substantially
increased standard deviation of the Purcell-enhancement with disorder, making
it increasingly likely to find collective excitation eigenmodes with very high
Purcell factors that are also stronger for magnetic than electric excitations.
We show that disorder can dramatically modify the cooperative response of the
metamaterial even in the presence of strong dissipation losses as is the case
for plasmonic systems. Our analysis in terms of collective eigenmodes paves a
way for controlled engineering of electromagnetic device functionalities based
on strongly interacting metamaterial arrays.
