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 imaging1. They also open alternative avenues for the management of light to improve the performance of photovoltaic cells2. Recent advances have demonstrated the feasibility of a giant refractive index in metamaterials at microwave and terahertz frequencies3,4, 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 K0.997Ta0.64Nb0.36:Li0.003 (KTN:Li) perovskite6-12, 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.