Low-temperature electrical and thermal resistivities of potassium: Deviations from Matthiessen's rule

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Abstract
The low-temperature electrical and thermal resistivities of potassium are calculated as functions of temperature and impurity concentration. Realistic phonon spectra are used for computing the electronphonon interaction. The variational calculation of the transport coefficients employs a trial distribution function which contains a nontrivial dependence on both the energy and the angular coordinates, so that deviations from Matthiessen's rule (DMR) in the electrical resistivity may be calculated to better accuracy than previously possible. Both the energy and the angular dependence are found to be relevant for the electrical resistivity, and the improved calculation gives good agreement with the experimentally observed DMR. For the thermal resistivity our results agree with previous ones; the angular dependence is found to be unimportant, and as a result we obtain essentially no improvement over calculations which use energy-dependent trial functions. The lack of agreement with the observed DMR in the thermal case tends to confirm the earlier conclusion that another mechanism is involved.