Evolution of the 7/2 Fractional Quantum Hall State in Two-Subband Systems

We report the evolution of the fractional quantum Hall state (FQHS) at a total Landau level (LL) filling factor of v = 7/2 in wide GaAs quantum wells in which electrons occupy two electric subbands. The data reveal subtle and distinct evolutions as a function of density, magnetic field tilt angle, or symmetry of the charge distribution. At intermediate tilt angles, for example, we observe a strengthening of the v = 7/2 FQHS. Moreover, in a well with asymmetric change distribution, there is a developing FQHS when the LL filling factor of the symmetric subband v(S) equals 5/2 while the antisymmetric subband has a filling factor of 1 < v(A) < 2.