New photorefractive mechanism in centrosymmetric crystals: A strain-coordinated Jahn-Teller relaxation

Abstract

We present observations and an explanation of a photorefractive effect in strained centrosymmetric KTN and KLTN crystals in the absence of an externally applied electric field. Centrosymmetric crystals are forbidden to display the classical photorefractive effect without application of an applied field. Nevertheless, in diffraction experiments, centrosymmetric KTN:Cu and KLTN:Cu crystals show index changes of p to 1.7\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ and photorefractive response at more than 120 \ifmmode^\circ\else\textdegree\fi{}C above the phase transition. Experiments described here allow us to conclude that a Jahn-Teller relaxation of the spatially modulated ${\mathrm{Cu}}^{2+}$ dopant concentration is responsible.