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 {μ}m. 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 ωc{τ} was as small as 2 at 40 ^∘{}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 {Γ} 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.