  Perovskites have been the focus of attention due to their multitude of
outstanding optoelectronic properties and structural versatility.
Two-dimensional halide perovskite such as (C_6H_5C_2H_4NH_3)_2PbI_4, or simply
PEPI, forms natural multiple quantum wells with enhanced light-matter
interactions, making them attractive systems for further investigation. This
work reports tunable splitting of exciton modes in PEPI resulting from strong
light-matter interactions, manifested as multiple dips (modes) in the
reflection spectra. While the origin of the redder mode is well understood,
that for the bluer dip at room temperature is still lacking. Here, it is
revealed that the presence of the multiple modes originates from an indirect
coupling between excitons in different quantum wells. The long-range
characteristic of the mediated coupling between excitons in distant quantum
wells is also demonstrated in a structure design along with its tunability.
Moreover, a device architecture involving an end silver layer enhances the two
excitonic modes and provides further tunability. Importantly, this work will
motivate the possibility of coupling of the excitonic modes with a confined
light mode in a microcavity to produce multiple exciton-polariton modes.
