High-Frequency Cyclotron Resonance in Lead and the Electron-Phonon Interaction

The frequency and temperature dependences of the electron-phonon interaction have been investigated in lead by the Azbel'-Kaner cyclotron-resonance technique. The experiments have been performed in the unusual millimeter and submillimeter microwave band from 70 to 500 GHz, corresponding to the wavelength 4 to 0.6 mm. In this frequency band the photon energy value, ω≤2 meV, is near the typical phonon energy in lead. The experiments were performed in the temperature range from 1.5 up to 6^∘{}K. The effective mass m* and relaxation time τ, measured on two different types of orbits, are frequency and temperature dependent. These dependences are directly related to the electron-phonon interaction. For both orbits m* is found to increase as the temperature squared and the frequency squared. The maximum relative increases are m*(5.4^∘K)m*(0^∘K)=1.03 and m*(457 GHz)m*(0 GHz)=1.008. The relaxation frequency τ^-1 dependence varies as the cube of both the temperature and the frequency. The theoretical dependences on T and ω are thus well confirmed, but the order of magnitude of the frequency effects is smaller than predicted.