Surface-Impedance Oscillations in a Weak Magnetic Field

We have made a detailed experimental study of the microwave surface resistance of high-purity metal single crystals in the regime of weak magnetic field. Samples of Sn, In, and Al show oscillatory variations of surface resistance that are periodic in reciprocal field. For a given fundamental resistance maximum at field $H_0$, successive peaks occur at $\frac{1}{3}{H}_0$, $\frac{1}{5}{H}_0$, $\frac{1}{7}{H}_0$, etc., i.e., all the odd submultiples of the field of the first resistance maximum. The oscillations are observed typically in fields of just a few Oe to about 100 Oe at a frequency of 35 Gc/sec. We have studied the anisotropy of the effect with orientation of magnetic field in a given sample plane, as well as the dependence of the effect on the sample plane in which a given direction is observed. The amplitude of the effect is found to be a function of the direction of the rf current. The effect is dependent on the experimental frequency. In the range of 28 to 70 Gc/sec, we find that a given resistance maximum moves to increased fields as ${{\omega }_{\mathrm{rf}}}^{\frac{3}{2}}$. Signals are readily observed also with the magnetic field tipped out of the sample plane. We suggest that the observed oscillations in the microwave absorption arise from variations with magnetic field of the time that the electron spends interacting with the electric fields in the surface region. This consideration leads us to suggest that the period of the oscillations is related to the values of radius of curvature and velocity of the electron at a single point on the Fermi surface.