Competition between lattice distortion and charge dynamics for the charge carriers of double-layered manganites

Abstract

We have investigated the characteristics of the charge carriers of the double-layered manganites, ${\mathrm{La}}_{2\ensuremath{-}2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}(x=0.35,$ 0.40), using polarized O $1s$ x-ray absorption spectroscopy. When the system undergoes the insulator to metal transition, the spectral weight is transferred to the absorption threshold, analogous to the Drude weight in optical absorption. The charge carriers in the metallic phase contain comparable amounts of in-plane and out-of-plane character. This result is due to the competition between the tetragonal lattice distortion and the charge dynamics that force the charge carriers out of and in the plane, respectively.