Effect of Landau-level mixing on quantum-liquid and solid states of two-dimensional hole systems

Measurements on dilute, low-disorder, two-dimensional hole systems at GaAs/AlxGa1-xAs interfaces reveal insulating behavior near different fractional quantum Hall liquid states. We interpret these insulating phases as pinned Wigner solid states and experimentally show that the filling factor around which they are observed moves to progressively smaller values as the areal hole density is increased. This dependence demonstrates the dramatic influence of Landau-level mixing, or the effective diluteness, on the liquid-solid transitions of a two-dimensional system.