Influence of Ortho-II structural phase on the 60 K plateau formation in YBa2Cu3O6+x
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In the present study, we have employed two dimensional ASYNNNI model to investigate how the Ortho-II structure formation influences doping, p, of the superconducting CuO2 planes in YBa2Cu3O6+x high-T-c superconductor. It was shown, that if the direct repulsive interaction between next nearest oxygen atoms (V-3), present in the Hamiltonian of the ASYNNNI model, is neglected, the Ortho-II ordering is destroyed and doping p becomes a linearly increasing function of oxygen concentration x in the range 0.50 LT = x LT = 0.65, for any choice of critical chain length l(cr) (defined so that CuO chains of length l LT l(cr) cannot transfer holes to the CuO2 planes). Consequently, the T-c(x) dependence, obtained by the employment of the universal T-c vs. p relation, does not exhibit experimentally observed 60 K plateau. The results presented here confirm that establishment of Ortho-II structural phase is a key factor for the 60 K plateau formation in the T-c(x) dependence. (C) 2012 Elsevier B. V. ...All rights reserved.