On the Critical Temperature of Superconductivity of La2-xSrxCuO4 Thin Films

Superconductivity of the cuprate La2-xSrxCuO4 thin films is considered within the concept of the preformed pairs (bipolarons). Taking the extended Holstein-Hubbard model as a basis for a strongly interacting hole-lattice system of the cuprate films, a relation between the temperature of Bose-Einstein condensation (T-BEC) of an ideal gas of the intersite bipolarons and the strains in the thin films is established. In doing that (relation), the chain model of cuprates, proposed by Alexandrov and Kornilovitch in ref. (Phys Rev Lett 82(4):807, 1999), is used. It is shown that the calculated values of the temperature of Bose-Einstein condensation of the bipolarons in the cuprate La2-xSrxCuO4 thin films grown on LaSrAlO4 and SrTiO3 substrates correlate (and at certain values of doping level x satisfactorily agree) with the experimental values of the critical temperature of superconductivity (T-c) of the above systems. The T-BEC versus x dependence obtained within the approach is very similar to the dome-shape type T-c versus x phase diagram of La2-xSrxCuO4 thin films. The obtained phase diagram has a feature of "1/8"-anomaly which is a common for both bulk and film samples of La2-xSrxCuO4.