Transport evidence of the lowest Landau-level spin-index anticrossing in (110) GaAs two-dimensional holes

An anomalous magnetoresistance peak is observed within the lowest Landau level (ν=1) of a two-dimensional hole system on (110) GaAs. We interpret this peak as the transport signature of a ±3/2 spin-reversal level anticrossing in the lowest Landau level. Temperature dependence of the peak height is consistent with thermal activation across an anticrossing gap. Persistent photoconductivity controllably shifts the peak to lower magnetic field by several tesla. Self-consistent calculations of the valence band mixing beyond the usual axial approximation allow the anticrossing magnetic field, anticrossing gap, and spin polarization to be evaluated as a function of average confinement electric field E. The confinement E necessary to explain the observed peak positions before and after illumination is consistent with a dilute photocharging of the substrate.