NIST Authors in **Bold**

Author(s): | V Crespi; Marvin Cohen; David R. Penn; |
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Title: | Anharmonic Phonons and the Isotope Effect in Superconductivity |

Published: | January 01, 1991 |

Abstract: | Anharmonic interionic potentials are examined in an Einstein model to study the unusual isotope-effect exponents for the high-T(c) oxides. The mass dependences of the electron-phonon coupling constant λ and the average phonon frequency square-root <ω2> are computed from weighted sums over the oscillator levels. The isotope-effect exponent is depressed below 1⁄2 by either a double-well potential or a potential with positive quadratic and quartic parts. Numerical solutions of Schrodinger's equation for double-well potentials produce lambda's in the range 1.5-4 for a material with a vanishing isotope-effect parameter-alpha. However, low phonon frequencies limit T(c) to roughly 15 K. A negative quartic perturbation to a harmonic well can increase-alpha above 1⁄2. In the extreme-strong-coupling limit, alpha is 1⁄2, regardless of anharmonicity. |

Citation: | Physical Review B (Condensed Matter and Materials Physics) |

Volume: | 43 |

Issue: | 16 |

Pages: | pp. 12921 - 12924 |

Research Areas: | Condensed Matter Physics |