Polarized X-Ray Absorption Fine Structure of La₂CuO_4−y Single Crystal

Abstract

Polarized Cu K X-ray absorption fine structure (XAFS) has been measured on a single crystal of undoped La₂CuO_4−y for the first time, using a fluorescence detection technique. The polarized near-edge structure and EXAFS were strongly anisotropic, demonstrating the quasi-two-dimensional nature of electron states and local structure. The polarization dependence of the near-edge structure confirms that the Cu atoms take 2+ valence or d⁹ configuration with a strong fourfold Cu–O1 bonds within the CuO₂ plane and weak twofold Cu–O2 bonds along the c-axis, which is consistent with the anisotropic local structure suggested by the Fourier transform of polarized EXAFS and a crystal structure.