Milli-Kelvin magneto-transport studies of two-dimensional hole systems under illumination

Abstract

We present evidence for the occurrence of an insulating phase both at zero and high magnetic fields, observed in extremely dilute two-dimensional hole systems in GaAsAl 1− x Ga x As quantum wells. At the highest hole concentrations the insulating phase is consistent with the magnetically-induced Wigner solid. As the hole concentration is persistently reduced by illumination of the structures, an insulator-metal-insulator transition develops in the magneto-transport around filling factor v = 1 and eventually the structure becomes insulating at all magnetic fields. The zero-field insulator emerges at a critical value of the dimensionless inter-particle separation, r s , of around 14, the highest value yet reported for this transition. We discuss these observations in the light of recent studies of the Wigner solid and the Hall insulator and invoke a model of the recombination kinetics of our experiments which accounts for the reduction in hole concentration under illumination.