We demonstrate that two-dimensional crystals made of active particles can
experience extremely large spontaneous deformations without melting. Using
particles mostly interacting via pairwise repulsive forces, we show that such
active crystals maintain long-range bond order and algebraically-decaying
positional order, but with an exponent η not limited by the 31
bound given by the (equilibrium) KTHNY theory. We rationalize our findings
using linear elastic theory and show the existence of two well-defined
effective temperatures quantifying respectively large-scale deformations and
bond-order fluctuations. The root of these phenomena lies in the sole
time-persistence of the intrinsic axes of particles, and they should thus be
observed in many different situations.Comment: 6 pages, 4 figure