Giant broadband refraction in the visible in a ferroelectric perovskite

In principle, materials with a broadband giant index of refraction ( n > 10) overcome chromatic aberration and shrink the diffraction limit down to the nanoscale, allowing new opportunities for nanoscopic imaging 1 . They also open alternative avenues for the management of light to improve the performance of photovoltaic cells 2 . Recent advances have demonstrated the feasibility of a giant refractive index in metamaterials at microwave and terahertz frequencies 3 , 4 , but the highest reported broadband index of refraction in the visible is n < 5 (ref. 5 ). Here, we report a ferroelectric perovskite with an index of refraction of n > 26 across the entire visible spectrum and demonstrate its behaviour using white-light and laser refraction and diffraction experiments. The sample, a solid-solution K 0.997 Ta 0.64 Nb 0.36 :Li 0.003 (KTN:Li) perovskite 6 – 12 , has a naturally occurring room-temperature phase that propagates visible light along its normal axis without significant diffraction or chromatic dispersion, irrespective of beam size, intensity and angle of incidence.