Observation of a Mass-Anisotropy-Driven Stripe Phase in Two Dimensions

Even-denominator fractional quantum Hall states observed in high quality two-dimensional (2D) electron systems in the first excited (N = 1) Landau level, such as the well-known ν = 5/2 state, are candidates for non-Abelian Moore-Read states. One possible application of such states is fault-tolerant topological quantum computing. Here we study a 2D electron system, confined to an AlAs quantum well, which exhibits a rich sequence of odd-denominator fractional quantum Hall states in the lowest (N = 0) Landau level. In the N = 1 Landau level, instead of a topologically ordered even-denominator fractional quantum Hall state, our experiments reveal an emergent stripe phase, signaling a spontaneous breakdown of the translational symmetry. Such symmetry-breaking can be attributed to the anisotropic effective mass of electrons in AlAs. Intriguingly, the stripes orient themselves along the smaller effective mass direction; this is consistent with the results of recent calculations [1]. We also find that these mass-anisotropy-induced stripes are quite robust; they cannot be reoriented by the application of a large in-plane magnetic field, and persist to high temperatures.

[1] Zheng Zhu, Inti Sodemann, D. N. Sheng, and Liang Fu, Phys. Rev. B 95, 201116(R) (2017).