Isotope effects in high-Tc cuprate superconductors as support for the bipolaron theory of superconductivity

We provide a unified parameter-free explanation of the observed oxygen-isotope effects on the critical temperature, the magnetic-field penetration depth and on the normal-state pseudogap for underdoped cuprate superconductors within the framework of the multi-(bi)polaron theory with strong Coulomb and Fröhlich interactions. We also quantitatively explain the measured critical temperature and the magnitude of the magnetic-field penetration depth. This paper thus represents an important support for the bipolaron theory of high-temperature superconductivity, compatible with many other independent observations. 4 Author to whom any correspondence should be addressed. New Journal of Physics 14 (2012) 013046 1367-2630/12/013046+10$33.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft