second-order (or weakly first order) transition results in a stripe phase. As for the $\nu=1/2$ case, this stripe becomes enhanced as $\alpha$ is further increased. Therefore, in $n\geq 2$ LLs mass anisotropy generally produces stripes, even when isotropic ground states have a tendency to forming a bubble phase.

![(Color online). Spectrum of $N_e=8$ electrons at $\nu=1+1/3$ with thickness $w=2\ell_B$. Inset: same spectrum plotted relative to the ground state at each $\alpha$. Unit cell has a rectangular shape with aspect ratio $3/4$.[]{data-label="fig_onethirdanisoll1w2.0"}](totalfullanisoll1w2.0rec0.75_8_24_reduced.eps){width="0.9\linewidth"}

$n=1$ Landau level: incompressible to compressible transitions driven by anisotropy
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In $n=1$ LL, $\nu=1/3$ state is significantly weaker than its $n=0$ LL counterpart, having an experimental gap an order of magnitude smaller and roughly the same as the gap of $\nu=1/2$ state. This has been anticipated in early numerical calculations that found the ground state of the Coulomb interaction projected to $n=1$ LL to be at the transition point between compressible and incompressible phases [@haldane_prange].

![(Color online). Guiding-center structure factor $S_0(\mathbf{q})$ for $\nu=1/3$ state in $n=1$ LL with thickness $w=2l_B$ and anisotropy $\alpha=0.4$ (a). For comparison, we also show $S_0(\mathbf{q})$ for the state with $\alpha=1.3$ which is in the Laughlin universality class (b). Two peaks in the response 