Anomalous magnetoresistance peak in (110) GaAs two-dimensional holes: Evidence for Landau-level spin-index anticrossings

We measure an anomalous magnetoresistance peak within the lowest Landau level (nu = 1) minimum of a two-dimensional hole system on (110) GaAs. Self-consistent calculations of the valence band mixing show that the two lowest spin-index Landau levels anticross in a perpendicular magnetic field B consistent with where the experimental peak is measured, Bp. The temperature dependence of the anomalous peak height is interpreted as an activated behavior across this anticrossing gap. Calculations of the spin polarization in the lowest Landau levels predict a rapid switch from about -3/2 to +3/2 spin at the anticrossing. The peak position Bp is shown to be affected by the confinement electrostatics, and the utility of a tunable anticrossing position for spintronics applications is discussed.