Schematic diagram of the two different square superlattice patterns after the discharge of small spots is extinguished. Panels (b) and (d) are schematic diagrams corresponding to panels (a) and (c), respectively. (b) The black areas are the centers of four small spots. (d) The large blue areas and the small blue areas represent the centers of the squares consisting of four vibrating filaments and the centers of antisymmetric stretching vibration, respectively. The arrows show the vibrations of each vibrating filament.