Anisotropy of the dielectric function in YBa2Cu3O6.

Kircher J., Alouani M., Garriga M., Murugaraj P., Maier J., Thomsen C., Cardona M., Andersen O.K., Jepsen O.

Experimental data for the anisotropy of the dielectric tensor epsilon = epsilon 1+i epsilon 2 in YBa2Cu3O6 are presented and interpreted. The spectra in the range between 1.7 and 5.2 eV were obtained by rotating-analyzer ellipsometry using a single crystal. It is found that the component of epsilon 2 in the ab plane ( epsilon 2a) displays a sharp peak at 4.1 eV, while the component along the c axis ( epsilon 2c) has a less pronounced peak at 3.8 eV, a small peak at 4.2 eV, and a broad maximum near 5 eV. Similar structures were found in the interband spectra calculated using the local-density approximation. The 4-eV optical structure is caused by nearly parallel initial- and final-state bands whose wave functions are located, respectively in the O-Cu-O dumbbells and in the BaO-Cu-OBa triple layers. Intraionic 3d to 4p transitions in dumbbell Cu contribute 90\% of the optical matrix elements.

Physical Review B, 40 7368-71, 1989.

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