Competition between fractional quantum Hall liquid and Wigner solid at small fillings: Role of layer thickness and Landau level mixing

The Wigner solid, an ordered-array of charges, and the fractional quantum Hall liquid, an incompressible state, compete in very clean (low disorder) two-dimensional (2D) electron systems at small Landau level fillings. Here we report magneto-transport data for a new 2D
electron system where the electrons are confined to an AlAs quantum well. The exceptionally high quality of the samples and the large electron effective mass allow us to determine the liquid-solid phase diagram for the 2D electrons in a large range of filling factors near 1/3 and 1/5. The data and their comparison with an available theoretical phase diagram reveal the crucial role of Landau level mixing and finite electron layer thickness in determining the prevailing ground states.