Influence of Ortho-II structural phase on the 60 K plateau formation in YBa2Cu3O6+x

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-Tc superconductor. It was shown, that if the direct repulsive interaction between next nearest oxygen atoms (V3), 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 ⩽ x ⩽ 0.65, for any choice of critical chain length lcr (defined so that CuO chains of length l < lcr cannot transfer holes to the CuO2 planes). Consequently, the Tc(x) dependence, obtained by the employment of the universal Tc 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 Tc(x) dependence.

► Oxygen ordering and superconducting properties of the YBa2Cu3O6+x superconductor. ► Study on the charge transfer from CuOx to CuO2 planes and doping calculation. ► Ortho-II ordering provides constant doping and 60 K plateau formation in Tc(x) curve. ► Average length of CuO chains determines shape of Tc(x) curve.