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Register a new userInterplay of Doping and Structural Modulation in Superconducting Bi2Sr2-xLaxCuO6+d thin films
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We have studied the evolution of the structural modulation in epitaxial, c-axis oriented, Bi2Sr2-xLaxCuO6+d thin films when varying the La content x and for a given x as a function of oxygen content. A series of thin films with 0<x<0.8 have been prepared in-situ by rf magnetron sputtering and characterized by R(T) measurements and RBS, TEM and X-Ray diffraction techniques. The oxygen content of each individual film was varied by thermal annealing across the phase diagram. The evolution of the structural modulation has been thoroughly studied by X-Ray diffraction in determining the variation of the amplitude of satellite reflections in special 2 axes 2theta /theta-theta scans (reciprocal space scans). It is shown that the amplitude of the modulation along the c-axis decreases strongly when x increases from 0 to 0.2. It is demonstrated that this variation is essentially governed by La content x and that changing the oxygen content by thermal treatments has a much lower influence, even becoming negligible for x>0.2. Such study is important to understand the electronical properties of Bi2Sr2-xLaxCuO6+d thin films.
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Bi2Sr2-xLaxCuO6+d and Bi2-yPbySr2-xLaxCuO6+d high-Tc superconductors in a wide doping range from overdoped to heavily underdoped were studied by X-ray absorption and photo-emission spectroscopy. The hole concentration p was determined by an analysis of the Cu L3-absorption edge. Besides the occupied density of states derived from photoemission, the un-occupied density of states was determined from the prepeak of the O K-absorption edge. Both, the occupied as well as the unoccupied density of states reveal the same dependence on hole doping, i.e. a continuous increase with increasing doping in the hole underdoped region and a constant density in the hole overdoped region. By comparing these results of single-layer BSLCO with previous results on single-layer LSCO it could be argued that besides the localized holes on Cu sites the CuO2-planes consist of two types of doped holes, from which the so-called mobile holes determine the intensity of the prepeak of the O 1s absorption edge.
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