Unconventional fractional quantum hall states in a wide quantum well

A bilayer electron system that is formed in a $60$-nm-wide GaAs quantum well and has a large difference of the electron densities in the layers has been studied. It has been found that, when a magnetic field is tilted from the normal to the plane of the system, integer quantum Hall effect states at the filling factors of Landau levels of $1$ and $2$ disappear; instead, fractional quantum Hall effect states in the interval between these filling factors appear at the filling factors $\nu_F=4/3, 10/7$, and $6/5$ with odd denominators and at the filling factor $\nu_F=5/4$. Several different states can be observed under the variation of the magnetic field. The detected fractional quantum Hall effect states are interpreted as combined states with the same filling factor 1 in the layer with the higher density and with the filling factors $\nu_F-1$ in the layer with the lower density. These states are formed because of the redistribution of electrons between the layers, which occurs under the variation of the magnetic field. The appearance of the state with the filling factor $\nu_F=5/4$ with the even denominator is presumably attributed to the dominance of the interlayer electron–electron interaction over the intralayer one for electrons in the layer with the lower density.