Fig. 3. Onset of domain formation: Euler-like buckling instability of polar bands.

(A to C) Snapshots of the time evolution of an initially nematic system with $(\mathrm{\varphi },{\tilde{\mathrm{\ell }}}_{\mathrm{p}},\tilde{L})=(0.66,10,40)$, for $t/{\mathrm{\tau }}_{\mathrm{R}}^0=0.1,0.2,0.3$, respectively. (D) Wavelength of the instability of polar-sorted bands as a function for varying persistence length and $(\mathrm{\varphi },\tilde{L},{\tilde{n}}_{\mathrm{m}})=(0.66,40,1)$. (E) Stability phase diagram for various active forces and persistence lengths with parameters $(\mathrm{\varphi },\tilde{L})=(0.66,20)$. The solid line separates different phases and indicates the stability limit of the banded phase.