Resistance Fluctuations in Composite Fermion State near Landau Level Filling Factor $\nu= 1/2$ in A Square Quantum Well
We have studied the magnetotransport near Landau level filling factor $\nu = 1/2$ in a GaAs-Al0.3Ga0.7As square quantum well (width 35 nm) in magnetic field up to 42 T and in a temperature range between 50 mK and 1.5 K. In low temperatures T < 200 mK, the Rxx exhibits a deep, strongly temperature-dependent minimum centered at $\nu = 1/2$. The concomitant Rxy is not strictly linear with magnetic field (B) and the first derivative of Rxy with respect to B shows a sharp cusp at $\nu = 1/2$, indicating a non-classical Hall effect. We verify these characteristics are being single-layer origin by applying an in-plane magnetic field or electrostatic gates. The data may signal frustrations in the composite fermion state towards $\nu = 1/2$ pairing in the quantum well where the electron layer thickness far exceeds the magnetic length.