  Optical cavities, resonant with vibrational or electronic transitions of
material within the cavity, enable control of light-matter interaction.
Previous studies have reported cavity-induced modifications of chemical
reactivity, fluorescence, phase behavior, and charge transport. Here, we
explore the effect of resonant cavity-phonon coupling on the transient
photoconductivity in a hybrid organic-inorganic perovskite. To this end, we
measure the ultrafast photoconductivity response of perovskite in a tunable
Fabry-Perot terahertz cavity, designed to be transparent for optical
excitation. The terahertz-cavity field-phonon interaction causes apparent Rabi
splitting between the perovskite phonon mode and the cavity mode. We explore
whether the cavity-phonon interaction affects the material electron-phonon
interaction by determining the charge carrier mobility through the
photoconductivity. Despite the apparent hybridization of cavity and phonon
modes, we show that the perovskite properties, in both ground (phonon response)
and excited (photoconductive response) states, remain unaffected by the tunable
light-matter interaction. Yet the response of the integral perovskite-terahertz
optical cavity system depends critically on the interaction strength of the
cavity with the phonon: the transient terahertz response to optical excitation
can be increased up to 3-fold by tuning the cavity-perovskite interaction
strength. These results enable tunable switches and frequency-controlled
induced transparency devices.
