Metal-insulator transition induced by oxygen isotope exchange in the magnetoresistive perovskite manganites

Article Abstract:

Researchers have investigated the perovskite manganites R1-xMxMnO3 (where R3+ is a rare earth cation, M is a doubly charged cation of large ionic radius and both R and M fill A positions of ABO3 perovskite lattice). Colossal magnetoresistance (CMR) takes place in the temperature range of the phase transitions resulting in the creation of a ferromagnetic phase. It seems likely that electron-photon coupling must play a vital role in the CMR manganites. The nature of the electron-photon coupling is responsible for the very large isotope effect.

Isotopes

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Giant oxygen isotope shift in the magnetoresistive perovskite La(sub 1-x)Ca(sub x)MnO(sub 3+y)

Article Abstract:

The magnetoresistance in the perovskite La(sub 0.8)Ca(sub 0.2)MnO(sub 3+y) is probably due to the large isotope shift of over 20 kelvin in the ferromagnetic transition temperature on replacing the oxygen atom, 16O, with 18O. The coupling of Jahn-Teller lattice defects with charge carriers produces the isotope shift. The ferromagnet SrRuO(sub 3) that has an insignificant Jahn-Teller effect shows no isotopic shift. This indicates that lattice distortions affect the magnetic and electric properties of perovskites.

Causes of, Electric properties, Materials, Ferromagnetic materials, Electric properties of materials

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Evidence for polaronic supercarriers in the copper oxide superconductors La (sub 2-x)Sr (sub x)CuO(sub 4)

Article Abstract:

The results of magnetization and thermal expansion measurements on samples of the copper oxide superconductor La(sub 2-x)Sr(sub x)CuO(sub 4) are discussed. These characterize the oxygen-isotope effects on the carrier density and on the in-plane penetration depth. Results also showed that polaronic charge carriers exist and condense into Cooper pairs in high-temperature superconductors. It was also confirmed that a strong Jahn-Teller effect can result in the formation of these polarons.

Polarons, Copper oxide superconductors, High temperature superconductivity

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