Thermodynamics of disordered carbon(1-x)copper(x) and silicon(1-x)gold(x) near the metal-insulator transition

Abstract

Measurements of the electron-phonon relaxation time are carried out, using both a direct and indirect method, in three dimensional films of C$\sb{1-x}$Cu$\sb x$ and Si$\sb{1-x}$Au$\sb x$ in the temperature range 0.3K-4K. The electron-phonon resistance and thermal boundary resistance are also measured.

The directly measured relaxation times for C$\sb{1-x}$Cu$\sb x$ can agree with theoretical predictions if a longitudinal sound speed similar to that of graphite and a longitudinal to transverse speed ratio similar to that of silicate glasses are used. The results for the Si$\sb{1-x}$Au$\sb x$ only qualitatively agree with theory. The measured thermal resistances are in reasonable agreement with other experiments.

Comparison of the direct and indirect measurements of the relaxation times reveal that the specific heat coefficient $\gamma$ behaves approximately like $T\sp{-.6}$ in C$\sb{1-x}$Cu$\sb x$ below 1K, in qualitative agreement with current theories describing the behavior of disordered, interacting electrons near the metal-insulator transition.