Investigation of the low-temperature thermoelectric properties of tungsten by a field-nulling technique

The thermoelectric dc transport properties of five single-crystal tungsten samples have been measured over the temperature range 1.2-7 K. In addition to the electrical resistivity, thermal resistivity, and thermoelectric power, a new thermoelectric function $G\mathrm{}\left(T\right)\mathrm{}$ was determined; the properties of this function and the method for measuring it are analyzed. Evidence for electron-phonon scattering was observed for both the electrical and thermal resistivity, appearing as a deviation from a quadratic temperature dependence usually associated with the electron-electron interaction. The thermoelectric coefficients $S\mathrm{}\left(T\right)\mathrm{}$ and $G\mathrm{}\left(T\right)\mathrm{}$ were positive below about 5 K for all samples with a sign reversal occurring at higher temperatures. Below 3 K, a marked impurity dependence in the thermoelectric properties was observed. No sample exhibited the characteristic temperature dependence of electron-electron scattering. The sign reversal at higher temperatures is attributed to the onset of a phonon-drag mechanism.