Two-dimensional hole-gas cyclotron line splitting in the extreme quantum regime

For a two-dimensional hole gas in $\frac{\mathrm{GaAs}}{{\mathrm{Ga}}_x{\mathrm{Al}}_{1-x}\mathrm{As}}$ in a strong quantizing magnetic field such that only one Landau level is occupied, a large splitting of the otherwise sharp cyclotron line is observed to occur at a magnetic field value which increases systematically with the areal hole density. The possible relationship of this phenomenon to anomalous cyclotron behavior observed in the two-dimensional electron gas, or an explanation in terms of an intrasubband Landau-level crossing, are discussed.