Quantum Interference and Optical Tuning of Self-Trapped Exciton State in Double Halide Perovskite

Self-trapped excitons (STEs), known for their unique radiative properties, have been harnessed in diverse photonic devices; however, their comprehensive understanding and manipulation remain elusive. In this study, we present novel experimental and theoretical evidence revealing the hybrid nature and optical tunability of STE state in Cs₂Ag_0.4Na_0.6InCl₆. The detection of the Fano resonance in laser energy-dependent Raman and photo-luminescence spectra indicates the emergence of an exciton-phonon hybrid state, arising from robust quantum interference between the discrete phonon and continuum exciton states. Moreover, we demonstrate continuous tuning of this hybrid state with the energy and intensity of the laser field. These findings lay the foundation for a comprehensive understanding of the nature of STE and their potential for state control.