Spin and valley degrees of freedom in materials without inversion symmetry promise previously unknown device functionalities, such as spin-valleytronics. Control of material symmetry with electric fields (ferroelectricity), while breaking additional symmetries, including mirror symmetry, could yield phenomena where chirality, spin, valley, and crystal potential are strongly coupled. Here we report the synthesis of a halide perovskite semiconductor that is simultaneously photoferroelectricity switchable and chiral. Spectroscopic and structural analysis, and first-principles calculations, determine the material to be a previously unknown low-dimensional hybrid perovskite (R)-(−)-1-cyclohexylethylammonium/(S)-(+)-1 cyclohexylethylammonium) PbI3. Optical and electrical measurements characterize its semiconducting, ferroelectric, switchable pyroelectricity and switchable photoferroelectric properties. Temperature dependent structural, dielectric and transport measurements reveal a ferroelectric-paraelectric phase transition. Circular dichroism spectroscopy confirms its chirality. The development of a material with such a combination of these properties will facilitate the exploration of phenomena such as electric field and chiral enantiomer–dependent Rashba-Dresselhaus splitting and circular photogalvanic effects.

Extraction of non-equilibrium hot carriers generated by plasmon decay in metallic nanostructures is an increasingly exciting prospect for utilizing plasmonic losses, but the search for optimum plasmonic materials with long-lived carriers is ongoing. Transition metal nitrides are an exciting class of new plasmonic materials with superior thermal and mechanical properties compared to conventional noble metals, but their suitability for plasmonic hot carrier applications remains unknown. Here, we present fully first-principles calculations of the plasmonic response, hot carrier generation and subsequent thermalization of all group IV, V and VI transition metal nitrides, fully accounting for direct and phonon-assisted transitions as well as electron-electron and electron-phonon scattering. We find the largest frequency ranges for plasmonic response in ZrN, HfN and WN, between those of gold and silver, while we predict strongest absorption in the visible spectrum for the VN, NbN and TaN. Hot carrier generation is dominated by direct transitions for most of the relevant energy range in all these nitrides, while phonon-assisted processes dominate only below 1 eV plasmon energies primarily for the group IV nitrides. Finally, we predict the maximum hot carrier lifetimes to be around 10 fs for group IV and VI nitrides, a factor of 3 -4 smaller than noble metals, due to strong electron-phonon scattering. However, we find longer carrier lifetimes for group V nitrides, comparable to silver for NbN and TaN, while exceeding 100 fs (twice that of silver) for VN, making them promising candidates for efficient hot carrier extraction.

Coupled resonator optical waveguides (CROWs) have shown theoretical promise as microoptical integrated gyroscopes with sensitivities exceeding comparably sized MEMS gyroscopes. Here, we analyze the effect of static disorder on the rotational sensitivity of a CROW gyroscope. Since CROWs consist of a onedimensional array of evanescently coupled ring-shaped microresonators, disorder includes random variations of the resonator optical path length and couplings between them resulting from manufacturing errors. We show that the rotational sensitivity of the CROW gyro is relatively stable with respect to variations in the interresonator coupling. By contrast, even modest fluctuations in the resonators' roundtrip optical path length result in substantially lower rotational sensitives. Finally, it is shown that while most random configurations of defects reduce the maximum sensitivity, there are particular configurations for which the rotation sensitivity is significantly higher than that of a CROW without disorder.

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