  Two-dimensional (2D) crystals made of active particles were shown recently to
be able to experience extremely large spontaneous deformations without melting.
The root of this phenomenon was argued to lie in the time-persistence of the
orientation of the intrinsic axes of particles. Here, we pursue this idea and
consider passive systems subjected to time-persistent external perturbations.
We first study a 2D XY model subjected to time-correlated noise and find that
it can remain quasi-ordered in spite of correlations decaying much faster than
allowed in equilibrium. We then study a simple model of a passive 2D crystal
immersed in a bath of active particles, and show that it can sustain large
deformations without melting.
