MoSi2N4: A 2D Regime with Strong Exciton-Phonon Coupling

The exciton and phonon strong coupling in functional materials is rich of physics and has promising applications in modern optoelectronics and photonics. However, the direct realization of strong exciton-phonon coupling without complex and well-designed resonator at room temperature is still a challenge in this topic associated with the Born-Oppenheimer approximation and constrained by the thermalized noise. Here, the enhancement of exciton-phonon coupling in 2D MoSi2N4 material is demonstrated by the near exciton resonance technique and first realization of the strong-coupling states of exciton and phonon in MoSi2N4 at room temperature. With the involving of three-band terms transition processes, the phonon scattering transition probability and exciton-phonon interaction are significantly enhanced. Then the strong coupling is reached which maintains high energy transfer efficiency between exciton and phonon supporting over ten phonon replicas at room temperature without introducing harsh resonant cavity. This work identifies that the 2D MoSi2N4 should be a promising strong-coupling system for exploring many-body quantum states with strong correlations and further applications in quantum systems, especially for exciton tailoring and room-temperature tunable exciton lasers.