Change in optical anisotropy with rotation of orbital stripe in a half-doped bilayer manganite

Abstract

We report an optical study of a half-doped bilayer manganite, $\mathrm{Pr}{({\mathrm{Sr}}_{0.1}{\mathrm{Ca}}_{0.9})}_{2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$, which shows spontaneous rotation of the orbital stripe with variation of temperature $(T)$ in a charge-orbital ordered phase. While the in-plane optical anisotropy is identified together with the initial formation of the charge-orbital ordering, it is reversed at a lower $T$, where the orbital stripe is rotated by 90\ifmmode^\circ\else\textdegree\fi{}. The change in optical anisotropy leads to anomalous $T$ dependence of electrodynamic parameters while keeping the orthorhombic lattice axes intact.