Theory of electron-phason scattering and the low-temperature resistivity of potassium

Scattering of electrons by phasons, the collective excitations of an incommensurate charge-density wave (CDW), is presented as a new mechanism in the low-temperature resistivity of potassium. It is shown to provide an explanation for recent precision measurements in potassium between 0.38 and 1.3 K, where conventional mechanisms, such as electron-electron scattering, fail. With this theory, it is possible to explain the shape of the measured resistivity curves, the magnitude of the temperature-dependent part of the resistivity, and the sample dependence. The sample dependence is explained since the measured electron-phason resistivity, which is much larger along the CDW wave vector $\overrightarrow{\mathrm{Q}}$ than perpendicular to it, depends on the $\overrightarrow{\mathrm{Q}}$-domain structure of a particular sample. Fitting this theory to these experiments yields the value for the phason temperature ${\Theta }_{\phi }=3.25\mathrm{}$ K and an approximate range of the anisotropy of the phason spectrum, $7.7\lesssim \left(\frac{1}{\eta }\right)\lesssim 9.7$.. Further resistivity measurements at ultralow temperatures are needed to test the hypothesis of electron-phason scattering, and, if this mechanism continues to show promise, to provide more accurate estimates for the phason parameters.