We report a spectroscopic investigation of potassium–lithium–tantalate–niobate (KTN:Li) across its room-temperature ferroelectric phase transition, when the sample manifests a supercrystal phase. Reflection and transmission results indicate an unexpected temperature-dependent enhancement of average index of refraction from 450 nm to 1100 nm, with no appreciable accompanying increase in absorption. Second-harmonic generation and phase-contrast imaging indicate that the enhancement is correlated to ferroelectric domains and highly localized at the supercrystal lattice sites. Implementing a two-component effective medium model, the response of each lattice site is found to be compatible with giant broadband refraction.
Bibliographical noteFunding Information:
This research was funded by the Sapienza-Ricerca di Ateneo 2020 and 2021 projects, the H2020 Fet project PhoQus, PRIN 2020 (Grant No. 2020X4T57A), the Israel Science Foundation (Grant No. 1960/16) and PNRR MUR project PE0000023-NQSTI.
© 2023 by the authors.
- giant refraction
- nanodisordered perovskite
- nonlinear optics