Controlling the electro-optic response of a semiconducting perovskite coupled to a phonon-resonant cavity.

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-Pérot 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's electron-phonon interaction by determining the charge-carrier mobility through 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 threefold by tuning the cavity-perovskite interaction strength. These results enable tunable switches and frequency-controlled induced transparency devices.

Accurate terahertz spectroscopy of supported thin films by precise substrate thickness correction.

We present a new approach for accurate terahertz time-domain spectroscopy of thin films deposited on dielectric substrates. Our approach relies on the simultaneous measurement of film and substrate, allowing for 15 nm-precise determination of the thickness variation between the sample and reference. Our approach allows for unprecedentedly accurate determination of the terahertz conductivity of the thin film. We demonstrate our approach on a 10 nm thin iron film deposited on a 500 µm MgO substrate. We determine the Drude momentum relaxation time in iron to within 0.15 fs uncertainty.