Fluctuation of the hole density of a slightly under-doped (Bi,Pb)2 Sr2CaCu2O8+δ single crystal studied by X-ray absorption spectroscopy

The effects of in-plane polarization change and temperature variation on the determination of the hole density for under-doped (Bi,Pb)-2212 single crystals by XAS have been studied. The XAS signal at the CuL3 edge (925 eV-940 eV) and O-K edge (525 eV-539 eV) was recorded under continuous rotation of the CuO2 plane by 180 degree with a minimum increment of 1.8 degree yielding experimentally an in-plane polarization dependence for the absorption signals at the respective thresholds and from that the in-plane angular dependence of the hole density (nH(φ)). Fermi's golden rule was then used for the evaluation of the in-plane polarization dependence showing unexpected polarization independence. Second, the polarisation geometry was kept fixed and spectra were taken from room temperature to 10 K with a decrement about 10 K. While the polarization dependence nH(φ) differed for the respective thresholds the temperature dependence showed less variation.