Short-Wavelength Cyclotron Waves and Electron Correlations in Potassium

Observations of the Azbel'-Kaner cyclotron resonance spectra in thick slabs of high-purity potassium metal have revealed additional oscillations on the high-field side of the fundamental resonance. These anomalies in the surface impedance correspond to turning points of the cyclotron-wave dispersion curve at wavelengths which are short compared to orbit radii. The behavior of the signals agrees quite well with free-electron theory and confirms the extremely oscillatory character of the extraordinary mode. The absence of deviations due to Fermi-liquid effects in our experiments is investigated, and in particular we show under what circumstances the Fermi-liquid parameter $A_1$ can be determined from these signals.