Eliashberg function. cap alpha. /sup 2/F (. omega. ) and phonon spectrum F (. omega. ). A simple model for an amorphous s-p superconductor
A simple expression of the Eliashberg function ..cap alpha../sup 2/F (..omega..) for an amorphous s-p superconductor is obtained. One finds that ..cap alpha../sup 2/F (..omega..) = (1/..omega..) ..sigma../sub q/ (L (q) + N (q))delta (..omega.. - ..omega../sub q/), where q includes the phonon branch index; N (q)/..omega../sub q/ is the N process which conserves ''lattice'' momentum; L (q)/..omega../sub q/ replaces the U process in the crystalline phase and it selects ''lattice'' momentum through the structure factor of the amorphous phase. Both L (q) and N (q) are evaluated using the Heine-Animalu pseudopotential form factor and experimental structure factor. A qualitative deconvolution of the phonon spectrum F (..omega..) from ..cap alpha../sup 2/F (..omega..) for four alloys is attempted. The main findings are: (i) Due to the nonconservation of ''lattice'' momentum in the conventional sense, ..cap alpha../sup 2/F (..omega..) depends linearly on ..omega.. in the low-..omega.. region, similar to Bergmann's results on disordered superconductors. The calculated first derivatives of ..cap alpha../sup 2/F (..omega..) are in good agreement with tunneling data on amorphous superconductors. (ii) The deconvoluted F (..omega..) are in better agreement with theoretical results obtained using the Morse potential than the Lennard-Jones potential. (iii) The Hopfield-McMillan parameter eta tends to decrease in the amorphous phase. Results (ii) and (iii) are discussed in terms of structural short-range order in the amorphous state. For the purpose of comparison, a similar calculation is made for crystalline Pb; it is found that there is no unambiguous enhanced ..cap alpha../sup 2/F (..omega..) in the low-..omega.. region.
- Research Organization:
- Department of Applied Physics, Stanford University, Stanford, California 94305
- OSTI ID:
- 6750649
- Journal Information:
- Phys. Rev., B; (United States), Journal Name: Phys. Rev., B; (United States) Vol. 18:1; ISSN PLRBA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360104 -- Metals & Alloys-- Physical Properties
656101* -- Solid State Physics-- Superconductivity-- General Theory-- (-1987)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AMORPHOUS STATE
CRYSTAL LATTICES
CRYSTAL STRUCTURE
ELEMENTS
GORKOV-ELIASHBERG THEORY
LEAD
METALS
ORDER-DISORDER TRANSFORMATIONS
PHASE TRANSFORMATIONS
PHONONS
QUASI PARTICLES
SUPERCONDUCTORS