Negative Temperature Derivative of Resistivity in Thin Potassium Samples: The Gurzhi Effect?

The resistivity of free-hanging K wires cooled in He gas varies anomalously with temperature when the diameter $d$ becomes comparable to the mean free path $l_{\mathrm{ei}}$ for scattering of electrons by impurities. Wires with $d\lesssim l_{\mathrm{ei}}$ display a negative $\frac{d\rho }{\mathrm{dT}}$ in the vicinity of 1 K. It is suggested that this is the first experimental evidence for an interaction between surface scattering and normal electron-electron scattering as first proposed by Gurzhi. The new data also show that previous explanations of K data of Rowlands et al. are inadequate.