Anomalous electrical resistivity of potassium below 0.35 K

Ultra-high-precision measurements of the resistivity of potassium to 70 mK reveal a closely GaAs-$T^2$ variation from 1 K down to about 0.35 K, below which the variation is slower than $T^2$. The $T^2$ behavior is consistent with simple electron-electron scattering with a mean coefficient of 2.4±0.2 fΩ m/${\mathrm{K}}^2$. The slower variation below 0.35 K represents new anomalous behavior which is not yet understood.