Interplay of doping and structural modulation in superconducting Bi2Sr2−xLaxCuO6+δ thin films

Abstract

We have studied the evolution of the structural modulation in epitaxial, c-axis-oriented, Bi2Sr2−xLaxCuO6+δ 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 has been prepared in situ by rf-magnetron sputtering and characterized by R(T) measurements, Rutherford backscattering spectroscopy, transmission electron microscopy, 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 two axes 2θ∕θ−θ 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+δ thin films.

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