Possible superconductivity mechanism in high-temperature superconductors

The formation temperature ($T^*\sim 135$ K) is determined in the Shubin-Vonsovski approximation for local electron pairs in the CuO$_2$ planes of YBa$_2$Cu$_3$O$_7$ crystal. This estimate is used to obtain the Coulomb pseudopotential $\mu ^*\approx-0.15$. In the presence of strong electron-phonon coupling ($\lambda \sim0.5$) and electron correlation in the electron pairing, the estimate of critical temperature $T_c\approx 99\,$K agrees, by the order of magnitude, with its experimental value. The calculated ratio $2\Delta/kT_c\approx4.13$ confirms the presence of strong electron pairing.