Ultrahigh-field hole cyclotron resonance absorption in In _1-xMn_xAs films

We have carried out an ultrahigh-field cyclotron resonance (CR) study of p-type In_1-xMn_xAs films, with Mn composition x ranging from 0 to 2.5%, grown on GaAs by low-temperature molecular-beam epitaxy. Pulsed magnetic fields up to 500 T were used to make cyclotron resonance observable in these low-mobility samples. Clear CR spectra have been observed for all the samples at high fields in the megagauss range and even at room temperature. It was found that the observed cyclotron masses are not significantly dependent on the Mn concentration, indicating a large number of itinerant, effective-mass-p-type holes rather than d-like holes exist. It further suggests that the p-d exchange mechanism is more favorable than the double exchange mechanism in this narrow gap InAs-based dilute magnetic semiconductor. In addition to the fundamental heavy-hole and light-hole cyclotron resonance absorption appearing near the high-magnetic-field quantum limit, we observed many inter-Landau-level absorption bands whose transition probabilities are strongly dependent on the sense of circular polarization of the incident light. It has been found that the detailed theoretical calculation in terms of the effective mass theory explains the most of the CR spectra quantitatively, including the polarization dependence.