Reversal of electromagnetically induced transparency spectrum in an X-ray planar cavity

Abstract Electromagnetically induced transparency (EIT) can greatly reduce the group velocity of light, which has extensive applications in optical sensing, optical storage, etc, and it has been widely studied in visible and microwave wavelengths. In the X-ray regime, EIT was realized in an X-ray thin-film planar cavity, while the detection of the transparency window in the reflection direction is not easy. Due to the interference between the bare cavity reflection and the nuclear resonance, the spectral line profile can be manipulated by adjusting the phases and amplitudes of different channels. By varying the thickness of the top layer, we demonstrate that in the X-ray regime, the spectral line can be transformed from a dip to a peak at the resonant window while maintaining the slow light effect. The slow light ability is evaluated by calculating the group velocity, the interaction strength, and the clarification of EIT and Autler Townes splitting (ATS). As the interaction strength increases, the X-ray cavity transitions from EIT to EIT-ATS crossover regime, which is consistent with the variation of group velocity. The present work would facilitate the detection of slow X-ray light using the cavity system and be helpful for the EIT and ATS clarification studies.