Anisotropy of inter-exciton interaction and pattern formation dynamics in photoinduced structural phase transitions

We study theoretically nonlinear nonequilibrium real-time dynamics of an optically excited many-exciton system in a two-dimensional insulator, and search for conditions under which excitons can proliferate efficiently to produce a macroscopic photoinduced structural phase transition (PIPT). To study this problem theoretically, we take a many-exciton system coupling strongly with Einstein-phonons, and numerically calculate the proliferation of excitons and the resultant domain patterns.In particular, we focus on the anisotropy of inter-exciton interaction, and compare a strong anisotropic case to a weak one. We have concluded that the anisotropic case leads to very efficient proliferation, and makes the final PIPT extensive and successful compared to isotropic cases.