Cyclotron resonance in copper by a calorimetric method

Azbel’-Kaner cyclotron resonance in copper at 136 Gc/s has been observed by a calorimetric method. Masses are presented with the magnetic field lying in a (112) plane and tipping effects investigated with the magnetic field along a <111> direction. Beyond a certain tip angle, the absorption exhibits a pronounced ‘negative magnetoresistance’ due to the removal of non­-stationary resonant orbits by tipping from the skin depth, and at smaller tip angles the resonant minima shift to lower fields as expected. The spectrometer was calibrated by a substitution method and the amplitude of the oscillations compared with theoretical estimates. Finally, a pronounced rise in absorption at low fields was observed, and arguments are presented that this is due to retardation effects.