Electron-phonon scattering in potassium at high magnetic fields

Abstract

We have measured the temperature dependence of both the zero-field resistivity and the transverse magnetoresistance of polycrystalline potassium wires (ϱ(300 K)/ϱ(4.2 K)=140 to 6000) in fieldsH≲35 kG and at temperaturesT≲4.2 K. Our principal findings are: 1) The presence of a large magnetic fieldH=35 kG does not alter the temperature dependence of ϱ from that observed atH=0; below 4.2 K theT-dependent part of the resistivities,ϱT (H=0) andϱT (H=35 kG), fit well to the function exp (−Θ*/T) with the same Θ*=23K. 2) Deviations from Matthiessen's rule are significantly reduced in a strong field so that the magnitude ofϱT (H=0) approaches that ofϱT (H=35 kG) as sample purity decreases. 3) The slope of the high-field linear magnetoresistance increases slightly (≲8%) from 1.5 K to 4.2 K. We attribute the exponential temperature dependence ofϱT (H) to the freezing out of electron-phonon umklapp processes as has been shown for the zero-field resistivity. The reduction in deviations from Matthiessen's rule at high fields can be understood within semiclassical theory, but the latter cannot explain the failure ofϱT (H) to saturate at high fields. A proposal by Young that electron-phonon umklapp scattering may contribute aT-dependent high-field linear magnetoresistance in potassium is considered.