Study of the Radio-Frequency Size Effect in Potassium

Abstract

An initial study of the radio-frequency size effect (RFSE) in potassium by Koch and Wagner revealed several interesting features which occurred on tilting the magnetic field out of the sample plane. We wish to report an independent investigation and interpretation of the RFSE in potassium. Because of increased sample purity and higher experimental frequencies (up to 35 MHz), a number of new features of the phenomenon have been observed in addition to the primary RFSE series. These new signals occur in the low-field range where sharply resolved signals are observed. The higher-field regime where oscillatory signals are observed has also been studied in detail. For exciting currents polarized perpendicular to the magnetic field, these oscillatory signals are observed to exhibit a cutoff which is a strong function of tilt. On the basis of these experiments, a geometrical model of the RFSE is proposed which differs significantly from that used by Koch and Wagner. The model successfully accounts for the tilt dependence of both the primary RFSE series and the newly resolved signals. Using currents polarized parallel to the magnetic field, signals were observed due to the transition from effective to ineffective electrons spanning the sample thickness. This transition occurs for electrons near the limiting point of the Fermi surface and provides a caliper for the orbits in this region. Studies of these orbits confirm the observation of Koch and Wagner that the Fermi surface is indeed spherical and not distorted in the vicinity of the limiting points by either a spin-density or a charge-density wave.