Spin waves in potassium and sodium at 80 GHz

Abstract

A comprehensive study of spin-wave excitations at a frequency of 80 GHz is reported for both potassium and sodium. Theoretical lineshape computations are fitted to experimental data obtained by the microwave transmission technique, thus enabling an accurate determination of the first three spin-dependent Landau Fermi-liquid parameters for the conduction electrons. The values obtained are B0=-0.292+or-0.007, B1=-0.073+or-0.012 and B2=0.00+or-0.01 for potassium and B0=-0.221+or-0.006, B1=-0.026+or-0.010 and B2=0.01+or-0.015 for sodium. The consistency of these numbers with earlier, lower-frequency measurements indicates no frequency dependence up to that of the present measurements. The fitting procedure is carried out over the temperature range 1.4-25K, allowing a measurement of the isotropic part of the momentum scattering rate for these temperatures. The temperature-dependent part of the scattering rate is thus found to be directly proportional to the ideal electrical resistivity over two and a half orders of magnitude for both metals. An anomalous and presently unidentified feature, having the appearance of another class of spin signals is observed in the vicinity of the electron spin resonance and the first couple of spin-wave modes. This feature is strongest in sodium and its variation with temperature is more in accord with the spin scattering time than the resistivity scattering time-it awaits a theoretical explanation.