The thermopower of amorphous Nb-Si near the metal-insulator transition

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Abstract
The authors present experimental thermopower data for amorphous Nb100-xSix (55>or=x>or=91) in the temperature range 4 K-280 K which extends through the metal/insulator transition. The higher Nb content samples clearly show metallic behaviour having a low temperature 'knee' attributed to electron-phonon mass enhancement. As the Nb concentration is reduced, deviations away from this behaviour are marked, the thermopower becoming largely independent of temperature. Further reduction of the Nb content causes the temperature dependence to return. At low temperatures, close to the metal/insulator transition, the thermopower appears to diverge and does not seem to conform to the universal behaviour described by Enderby and Barnes (1990). This is probably because the density of states is still large at the Fermi energy and there is an appreciable hopping contribution to the conductivity.

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