Bipolaronic proximity and other unconventional effects in cuprate superconductors

TL;DR

This paper reviews evidence for strong electron-phonon interactions and bipolaronic mechanisms in cuprate superconductors, suggesting they may not be conventional BCS superconductors but involve Bose-Einstein condensation of bipolarons.

Contribution

It introduces the bipolaron theory to explain unconventional effects and phenomena observed in cuprate superconductors, highlighting a non-BCS mechanism.

Findings

Evidence of strong electron-phonon interaction in cuprates

Observation of checkerboard modulations of the order parameter

Detection of quantum magneto-oscillations in cuprates

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.