and bubbles take over. In this Section we discuss the effects of anisotropy on FQH states in higher LLs, focusing on fillings $\nu=1/3$ and $1/2$. Because of closer energy scales, we find that moderate changes in the anisotropy induce phase transitions between compressible and incompressible phases.

$n \geq 2$ Landau levels: stripes and bubbles {#ll2}
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![(Color online). Energy spectrum of $\nu=1/3$ (left) and $\nu=1/2$ filled $n=2$ LL (right): mass anisotropy establishes and reinforces the stripe order.[]{data-label="fig_ll2"}](totalll2rec0.75_reduced.eps){width="0.95\linewidth"}

In $n=2$ LL and higher, isotropic FQH states are energetically less favorable than stripe and bubble phases at filling $\nu=n+1/2$ and $\nu=n+1/3$, respectively. In Fig. \[fig\_ll2\] we show the energy spectrum (in units of $e^2/\epsilon\ell_B$) as a function of anisotropy $\alpha$ (we set the angle $\phi$ to zero). Energies are plotted relative to the ground state at each $\alpha$, and we chose the relatively modest system sizes ($N_e=8$ and 10 electrons) to facilitate comparison with the existing isotropic data in the literature [@edduncanky_stripe; @edduncanky_bubble]. The aspect ratio is set to the optimal values for the appearance of stripes or bubbles (see Refs.  and ).

As we see on the right panel of Fig. \[fig\_ll2\], at $\nu=1/2$ the presence of mass anisotropy reinforces the 