POLARIZED X-RAY-ABSORPTION STUDY OF TL2BA2CACU2O8 AND TL2BA2CA2CU3O10

Polarization-dependent measurements of the 0 ls absorption edges of Tl 2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10 single crystals have been performed. T hey give evidence for an increase of the unoccupied 0 2p(x,y) density of states per unit cell close to the Fermi level related to the CuO2 p lanes by a factor of 1.5 by insertion of the third CuO2 plane. This le ads to additional charge transfer to the Tl2O2 and Ba2O2 layers of the se self-doped systems. The average number of doped holes per CuO2 plan e and per formula unit for both materials is found to be close to othe r p-type doped cuprate superconductors with optimized superconducting transition temperature. From the Cu 2p3/2 edge Of Tl2Ba2Ca2Cu3O10, a s mall admixture of 12+/-2% of unoccupied states with 3d(3z2-r2) charact er to the empty Cu 3d states close to the Fermi level with predominant ly 3d(x2-y2) symmetry was found.