Fractional Quantum Hall effect in Ultra-high Quality Few-layer Black Phosphorus Transistors*

Black phosphorus(BP), as the only non-carbon elemental layered allotrope, has been investigated intensively because of its possession of high mobility and tunable gap. Here we report the fabrication of few-layer BP field effect transistor with mobility up to 55,000 cm²/Vs, and observation of two fractional QH states at filling factors n ~ -4/3 and -0.56 ± 0.1, underscoring BP as a tunable 2D platform for exploring electron interactions.