Superconducting Thin Films, Composites and Functions
Interim technical rept. 1 Oct 1984-31 Mar 1985
STANFORD UNIV CA DEPT OF APPLIED PHYSICS
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The important issue of how the superconducting transition temperature Tc in disordered systems changes near the M-I transition where strong localization is expected has been studied in the Mo-Ge system. In the high Mo concentration, which is in the weakly localized regime, Tc decreases linearly with decreasing Mo concentration from 7.5 K 78 at Mo at a rate of 0.18 Kat Mo. In this region the ratio of electron-phonon coupling constant Lambda to the bare density of states Mb 0 is constant, which is consistent with the Varma- Dynes tight-binding model. An extrapolation of the linear behavior of Tc in this regime yields the disappearance of Tc near 35 at Mo. However, measurements show that Tc exists down to 13.5 at Mo. A non-superconducting metallic phase is found to exist between 13.5 at 10.4 at Mo at which concentration the insulating phase occurs.
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