Modification of Surface Mode Frequencies and Superconductivity Tc by Adsorbed Layers
There is evidence that the enhancement of the superconducting transition temperature T c in amorphous or disordered films1 is caused by a decrease in the phonon frequencies relative to those in the bulk2,3 or, alternatively, by a change in the electron-phonon coupling constant α 2 (ω) relative to that in the bulk.4,5 It has been suggested that true surface phonons† as well as disorder may be responsible for the enhancement in sufficiently thin films,6,7 and theoretical calculations for model films7,8 lend support to this hypothesis. However, no unambiguous experimental evidence has been reported in favor of this hypothesis,‡ and in recent studies9,10 it has been emphasized that neither surface phonons nor any mechanism other than disorder within the films is needed to explain the experimental results.
KeywordsTransition Curve Effective Force Residual Resistance Surface Phonon Clean Film
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