Susceptibility of Polar Flocks to Spatial Anisotropy
Abstract
We consider the effect of spatial anisotropy on polar flocks by investigating active q-state clock models in two dimensions. In contrast to what happens in equilibrium, we find that, in the large-size limit, any amount of anisotropy changes drastically the phenomenology of the rotationally-invariant case, destroying long-range correlations, pinning the direction of global order, and transforming the traveling bands of the coexistence phase into a single moving domain. All this happens beyond a lengthscale that diverges in the q∞ limit. A phenomenology akin to that of the Vicsek model can thus be observed in a finite system for large enough values of q. We provide a scaling argument which rationalizes why anisotropy has so different effects in the passive and active cases.