Anharmonic phonons and the isotope effect in superconductivity
- Department of Physics, University of California at Berkeley, Berkeley, CA (USA) Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA (USA)
- National Institute of Standards and Technology, Gaithersburg, MD (USA)
Anharmonic interionic potentials are examined in an Einstein model to study the unusual isotope-effect exponents for the high-{ital T}{sub {ital c}} oxides. The mass dependences of the electron-phonon coupling constant {lambda} and the average phonon frequency {radical}{l angle}{omega}{sup 2}{r angle} 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 Schroedinger'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 {ital T}{sub {ital 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.
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 5661908
- Journal Information:
- Physical Review, B: Condensed Matter; (USA), Journal Name: Physical Review, B: Condensed Matter; (USA) Vol. 43:16; ISSN 0163-1829; ISSN PRBMD
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANHARMONIC OSCILLATORS
CRITICAL TEMPERATURE
DEBYE-WALLER FACTOR
ELECTRON-PHONON COUPLING
ELECTRONIC EQUIPMENT
EQUIPMENT
GORKOV-ELIASHBERG THEORY
HIGH-TC SUPERCONDUCTORS
ISOTOPE EFFECTS
OSCILLATORS
PHYSICAL PROPERTIES
SUPERCONDUCTORS
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE