Origin of the ν=1/2 fractional quantum Hall state in wide single quantum wells

We study the effect of subband energy separation and asymmetry on the quasiparticle excitation gaps of the ν=1/2 and coexisting fractional quantum Hall (FQH) states in wide single quantum wells. A new even-denominator FQH state at ν=3/2 and a dramatic subband-mixing-driven phase transition from a one- to two-component FQH state at ν=2/3 are observed. Our results reveal the two-component origin of the ν=1/2 FQH state, and allow us to construct an experimental phase diagram for electron states at half filling.