Physics – Condensed Matter – Superconductivity
Scientific paper
2008-09-21
Physics
Condensed Matter
Superconductivity
10 pages, 5 figures
Scientific paper
Strong electron correlations are responsible both for the insulator ground state of undoped La$_2$CuO$_4$ and strong antiferromagnetic coupling $J$ between neighbouring spins. We consider magnetic mechanism of superconducting pairing in the effective low energy $t - t' - t" - J^*$ model with all parameters calculated {\it ab initio}. Interaction of strongly correlated electrons with different phonon modes is also incorporated. In a BCS type theory the $d_{x^2 - y^2}$ gap is given by a sum of magnetic and phonon contributions. The phonon coupling parameter $\lambda = f(x)G$, where $G$ is a combination of bare electron-phonon couplings for all modes and the function $f$ depends on the hole concentration $x$ due to strong electron correlations. The main contribution to the only fitting parameter $G$ is determined by a competition of the breathing and buckling modes. Fitting the parameter $G$ from the isotope effect we obtain that magnetic and phonon contributions to the critical temperature $T_c $ work together and are of the same order of magnitude.
Ovchinnikov Sergei G.
Shneyder E. I.
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