Optical Spectroscopic Study of Layered Manganites with Charge-Orbital Ordering

초록

We review optical studies of the in-plane optical anisotropy in the charge-orbital ordered manganites with layered structure, a single-layer manganite Eu(1/2)Ca(3/2)MnO(4) (ECMO-214) and a bilayer manganite Pr(Sr(0.1)Ca(0.9))(2)Mn(2)O(7) (PSCMO-327). From the polarization-dependent optical measurements performed for single domain samples, both compounds are found to show in-plane anisotropy: the optical spectra with light polarized along the orbital chain direction exhibit a smaller energy gap state than those with the light polarized along the orbital stripe direction. Notably, different from the case of ECMO-214 with a single transition, the optical spectra of the PSCMO-327 compound exhibit a non-monotonic temperature-dependent evolution of the optical anisotropy, which is attributed to a spontaneous rotation of the orbital stripe. Our study clearly manifests that the orbital stripe is a parameter of the anisotropy of the physical properties in a charge-orbital ordered state.