Bipolaronic proximity and other unconventional effects in cuprate superconductors

Abstract

There is compelling evidence for a strong electron-phonon interaction (EPI) in cuprate superconductors from the isotope effects on the supercarrier mass, high resolution angle resolved photoemission spectroscopies (ARPES), a number of optical and neutron-scattering measurements in accordance with our prediction of high-temperature superconductivity in polaronic liquids. A number of observations point to the possibility that high-Tc cuprate superconductors may not be conventional Bardeen-Cooper-Schrieffer (BCS) superconductors, but rather derive from the Bose-Einstein condensation (BEC) of real-space pairs, which are mobile small bipolarons. Here I review the bipolaron theory of unconventional proximity effects, the symmetry and checkerboard modulations of the order parameter and quantum magneto-oscillations discovered recently in cuprates.