In multilayer quantum Hall systems, when the layer separation is sufficiently small, the interplay between intralayer and interlayer Coulomb interactions can lead to exotic, multicomponent, many-body states. A particular example is the even-denominator fractional quantum Hall state at total filling factor $\nu =1/2$ in bilayer systems with negligible interlayer tunneling. This state can be understood as a generalized Laughlin state described by the Halperin-Laughlin ${\mathrm{\Psi }}_{331}$ wave function. While such correlated states have been extensively explored in bilayers, little is known about their counterparts in systems with more than two layers. Here, we investigate a trilayer two-dimensional electron system confined to ultrahigh-quality GaAs triple quantum wells. We observe an exotic fractional quantum Hall state at total filling factor $\nu =5/7$, evinced by a deep longitudinal resistance minimum and a quantized Hall plateau, when the side layers have a density larger than the middle layer and $d/l_B\simeq 2.2$ ($d$ is the interlayer distance and $l_B$ the magnetic length). This state is naturally interpreted as the long-predicted trilayer, generalized Laughlin (${\mathrm{\Psi }}_{33311}$) state, characterized by $\nu =1/3$-like intralayer correlation within each layer and $\nu =1$-like interlayer correlation between neighboring layers. Our observation establishes a new member of the Halperin-Laughlin many-body states that extends interlayer coherence to three coupled layers.

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• Anyons
• Composite fermions
• Fractional quantum Hall effect
• Quantum wells
• Two-dimensional electron system
• Wigner crystal