Tilt exciton in two-dimensional perovskites and its nonlinear interaction

The realization of strong exciton-exciton interactions has garnered widespread attention in recent years because it plays a fundamental role in the field of modern condensed matter physics, such as in BEC and BEC-BCS crossover systems. We have confirmed the existence of tilt exciton in two-dimensional organic-inorganic perovskite systems and established that their interaction strength is two orders of magnitude greater than that in bilayer transition metal sulfide Moiré superlattices. The formation of tilt exciton requires the two-dimensional organic-inorganic perovskites surface relaxation, resulting the octahedral tilting in the outer layers which separates the electron and hole from the same layer, similar to the interlayer exciton. Tilt exciton possess lower energy, weaker absorption, and longer lifetimes compared to intrinsic exciton, their pristine counterparts. Furthermore, through Fourier imaging techniques, we have confirmed similar polarization modes for these two exciton species. Our findings provide a novel platform for research in many-body effects of macroscopic quantum phenomena.