Possible stripe phase at ν=7/3 in the presence of mass anisotropy

We study the phase diagram of ν=7/3 in the n=1 Landau level in the presence of a (two-fold) mass anisotropy. Using the density matrix renormalization group method on an infinite cylinder geometry with varying circumference, we find a continuous transition from the Laughlin fractional quantum Hall state to a stripe phase with a period of ~ 5.5l_B. The transition is driven by the condensation of the magnetoroton which becomes gapless at the critical point. The transition, in principle, could survive in the 2D limit and be observed in experiments.