Multiple Reflections in Gantmakher-Kaner Oscillations

Gantmakher-Kaner oscillations in gallium have been observed at 1.3°K at 9.2 GHz in the transmission mode for the field-normal case in addition to angles well away from the normal. A set of Gantmakher-Kaner oscillations with striking properties and a very small period has been associated with electrons on a small "approximately ellipsoidal" Fermi surface piece oriented along $k_b$. These oscillations have harmonic content which provides direct evidence for multiple reflections in the gallium slab indicating specular surface scattering for these particular electrons. A dramatic disappearance of just the fundamental as the dc field is decreased below the cyclotron resonance field cannot be explained by current theories of Gantmakher-Kaner oscillations.