Abstract
Photoinduced high-density phase of exciton masses excited at a two-dimensional stacking fault interface in BiI 3 has been studied by measuring the energy spectra of the degenerate four-wave-mixing (DFWM) signals and their excitation spectra using a nano-second laser with a very narrow line width. An energy splitting structure on the'DFWM spectra shows a repulsive interaction between excitons. Furthermore, multiple fine structures appearing in the excitation spectra of DFWM signals under the higher density suggest multiple exciton interactions in the condensates.