High-order two-component fractional quantum Hall states in GaAs quantum wells

Two-component fractional quantum Hall (FQH) states have been known to occur in double and wide quantum wells for nearly three decades. The simplest of these states occurs at a total filling factor ν = 2/3 = (1/3,1/3), where 1/3 is the filling factor of each component (layer). Of special interest are so-called unbalanced states which indicate that it might be energetically favorable to have FQH states at different filling factors in each layer. To date, only a few such states have been observed, including ν = 11/15 = (1/3, 2/5), 19/15 = (2/3, 3/5), and 29/35 = (2/5, 3/7). Here, we report experimental evidence for many more higher-order fractions, up to ν = 109/99 = (5/9, 6/11) and 106/117 = (4/9, 6/13). These states emerge upon application of in-plane magnetic fields, but in contrast to earlier studies, we employ “normal,” single-subband quantum wells. The presence of many states allows us to investigate the role of imbalance. Surprisingly, we find that quite often unbalanced states are noticeably stronger than the neighboring balanced states.