Larmor Waves in Copper and Cyclotron Waves in Sodium and Potassium at 80 GHZ.

Two classes of transmission signals in thin slabs of pure metal were investigated at low temperatures using an 80 GHz spectrometer. One type of signal is associated with collective modes of cyclotron motion of the conduction electrons, known as Cyclotron Waves. The other is a phenomenon associated with the phase of the individual spins of the electrons, which is known as Larmor Waves. A comprehensive study of ordinary and extraordinary cyclotron-wave modes was done on Sodium (Na) and Potassium (K). The exact combination of modes observed depended on the subharmonic, omegatau (the driving frequency times the momentum scattering time), and the sample thickness. As omegatau was large (100 to 150) for the samples used, it was possible to make observations as far as the fourth subharmonic. This enabled us to accurately predict the values for the spin-independent Landau Fermi-liquid parameters A_2 and A_3 for both metals, as well as estimate A_4 and A_5 for Potassium. The values obtained in this study were: A_2 (K) = -0.0283 +/-.0005; A_3(K) = -0.0007 +/-.0030 A_2(Na) = -0.0253 +/-.0005; A_3(Na) = -0.008 +/-.003. These values compare favorably with previous determinations as well as with theoretical predictions. In addition, the A_1 value for both Sodium and Potassium was estimated by using an appropriate sum role for the Laudau Fermi-liquid parameters. Larmor waves were studied in single-crystal Copper samples and a polycrystalline sample as a function of temperature. The measured Larmor-wave periods for the three crystal directions <100>, <110>,m and <111> were functions of the temperature, in contrast to that observed at 9 GHz, where no appreciable temperature dependence was found. However, at the high-temperature limit, the periods for the three crystal directions were comparable with the theoretical estimates, as well as with the observations done at 9 GHz. The observed amplitudes of the LW signals on the high-magnetic-field side of the conduction electron spin resonance were considerably larger than that on the low-field side, in the < 110> and < 111> direction samples at low temperatures. This asymmetry was not seen at 9 GHz. The variation of the periods of the oscillations with temperature and the asymmetry in the amplitudes of the Larmor-wave signals may be due to the presence of many -body effects (i.e., large omegatau value) and the non-sphericity of the Fermi surface of Cu.