New Observations in the $N\ge1$ Landau Levels of Wide GaAs Quantum Wells

We have studied a series of high-quality wide GaAs/AlGaAs quantum wells at various tilt angles ($\theta$) with respect to magnetic field. Several interesting observations have been made when the Landau level index is $N\ge1$. The quantum Hall states corresponding to total odd filling factors are seen to be reentrant with increasing $\theta$, i.e. they disappear and reemerge as $\theta$ is increased. This observation can be explained by considering oscillations in the tunnelling amplitude with increasing $\theta$. As $\theta$ is increased further, anisotropy emerges at values of half filling. This is particularly visible in the $N=1$ Landau level at total filling factors $\nu=9/2$ and $11/2$. For even larger values of $\theta$, anisotropy develops at $\nu=5$ followed by $\nu=7$. We will discuss how each of these observations are effected by quantum well width and also in the context of previous theoretical and experimental results.