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

Abstract

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