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U.S. Department of Energy
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Superconductivity of the A15 compound niobium aluminum

Thesis/Dissertation ·
OSTI ID:5617319
The microscopic superconducting properties of the metastable high transition temperatue A15 compound Niobium Aluminum are investigated in this work to further understand the origins of the high transition temperature in the A15 superconductors as a whole class. Material synthesis on A15 thin films has been carried out using electron-beam coevaporation to determine the A15 phase equilibrium and to establish the conditions of preparing homogeneous materials. Superconducting tunneling into high-quality, Nb-Al junctions is used to diagnose the material properties of the A15 Niobium Aluminum and shows that it is strongly electron-phonon coupled only when the composition approaches the A15 phase boundary. Tunneling spectroscopy analysis gives striking evidence of mode-softening mechanism responsible for the stronger coupling and the higher transition temperature. Upper critical field analysis suggests the relative unimportance of the electronic band density of states near the Fermi level in contributing to the variation of the transition temperature with the structure disorder in Nb-Al as has been generally assumed. Both the strong electron-phonon interaction and the induced soft lattice are equally important factors in giving the high transition temperature of most A15 superconductors.
OSTI ID:
5617319
Country of Publication:
United States
Language:
English