Effect of strong electron–phonon interaction on the nonphonon mechanism of superconductivity

The change in the critical temperature of a superconductor due to the electron-phonon interaction (EPI) is calculated. The isotopic effect exponent α is found to be smaller than that obtained in the BCS theory; it differs from the classical value of 1/2 the more strongly, the higher the value of the ratio of the critical temperature Tc to the Debye temperature ΘD. The correction to the tunnel density of states of the superconductor is calculated, which is connected with the EPI characteristic function g(ω) and makes it possible to reconstruct this function through the measurement of the voltage dependence of the differential conductivity (the electron–phonon interaction spectroscopy of high-Tc superconductors).

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