HIGH-FIELD CYCLOTRON-RESONANCE AND VALENCE-BAND STRUCTURE IN SEMICONDUCTING DIAMOND

The cyclotron resonance of thermally excited free holes has been observed in synthetic semiconducting diamond at ultrahigh magnetic fields up to 150 T generated by the single-turn-coil technique with pulsed far-infrared laser radiations of 28, 36, and 119 mum. Three absorption peaks were observed at and above room temperature for the magnetic fields parallel to the [100), [111], and [110) crystallographic directions. The typical value of omega(c)tau was as small as 2 at 40-degrees-C even in ultrahigh fields. One of the three peaks was observed in the cyclotron-resonance inactive circular polarization for holes, while the other two lines were observed in cyclotron-resonance active circular polarization for holes. Assuming that these resonance absorption lines are due to three holes of the valence bands at the GAMMA point, i.e., light-hole, heavy-hole, amd split-off-hole, we can conclude that the band dispersion curve for one of the three bands has a negative (electronlike) curvature in some directions.