Isotope effects in high-Tc cuprate superconductors: Ultimate proof for bipolaron theory of superconductivity

TL;DR

This paper provides comprehensive, parameter-free evidence supporting the bipolaron theory as the correct microscopic explanation for high-temperature superconductivity in cuprates, explaining isotope effects and other key properties.

Contribution

It offers the first unified, parameter-free explanation of isotope effects and critical properties in cuprates within the bipolaron framework, confirming its validity.

Findings

Quantitative match with measured critical temperatures

Explanation of isotope effects on pseudogap and penetration depth

Validation of bipolaron theory as the ultimate explanation

Abstract

Developing a theory of high-temperature superconductivity in copper oxides is one of the outstanding problems in physics. Twenty-five years after its discovery, no consensus on the microscopic theory has been reached despite tremendous theoretical and experimental efforts. Attempts to understand this problem are hindered by the subtle interplay among a few mechanisms and the presence of several nearly degenerate and competing phases in these systems. Here we provide 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 bipolaron theory compatible with the strong Coulomb and Froehlich interactions, and with many other independent observations in these highly polarizable doped insulators. Remarkably, we also quantitatively explain measured critical temperatures and magnitudes of the magnetic-field penetration depth. The present work thus represents an ultimate proof of the bipolaron theory of high-temperature superconductivity, which takes into account essential Coulomb and electron-phonon interactions.