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

We report an optical study of a half-doped bilayer manganite, Pr(Sr0.1Ca0.9)(2)Mn2O7, 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 degrees. The change in optical anisotropy leads to anomalous T dependence of electrodynamic parameters while keeping the orthorhombic lattice axes intact.