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) and_ϱT (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 of_ϱT (H=0) approaches that of_ϱT (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 of_ϱT (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 of_ϱT (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.