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 μm. 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 ω_cτ 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.