Polarons in Colossal Magnetoresistive and High-Temperature Superconducting Materials

Abstract

We review some unconventional oxygen-isotope effects in colossal magnetoresistive manganites and high temperature superconducting cuprates to assess the role of electron-phonon coupling in the basic physics of these materials. These include the unconventional oxygen-isotope effects on the Curie temperature and electrical transport in doped ferromagnetic manganites, on the supercarrier mass of superconducting cuprates, and on the antiferromagnetic ordering temperature of undoped parent cuprates. These unconventional isotope effects clearly demonstrate that the formation of polarons/bipolarons due to strong electron-phonon coupling is relevant to the basic physics of these materials and may be important for the occurrence of colossal magnetoresistance and high-temperature superconductivity. We also identify the phonon modes that are strongly coupled to conduction electrons from the angle-resolved photoemission spectroscopy, tunneling spectra, and optical data of doped cuprates. We consistently show a strong electron-phonon coupling feature at about 20 meV along the antinodal direction, which should also be important to the pairing mechanism of high-temperature superconductivity.