Emergent phases in nearly degenerate Landau levels of the state-of-the-art GaAs quantum wells

Semiconductor GaAs/AlGaAs-based 2D systems, famous for first observations of fractional quantum Hall (FQH) effects, stripe and bubble phases, microwave–induced resistance oscillations/zero-resistance states, and excitonic Bose condensates, continue to attract interest and bring more surprises. In our recent studies we have employed an in-plane magnetic field to bring Landau levels close to degeneracy in the state-of-the-art GaAs quantum wells [1] and observed several emergent phases. First, the talk will report observation of a highly anisotropic phase which emerges in the vicinity of filling factor 7/3. While reminiscent of quantum Hall stripe phases in high half-filled Landau levels (commonly found at filling factors 9/2, 11/2, 13/2, …), this phase emerges only in a narrow range of in-plane magnetic fields. Second, the talk will discuss uncorrelated two-component FQH states, some of which have been previously observed in wide quantum wells, in which the second electrical subband was occupied in a purely perpendicular magnetic field. However, many more higher-order fractions (such as 109/99 and 106/117) have emerged in our experiments using “normal”, single-subband quantum wells. Finally, the talk will presenty evidence for unconventional FQH states at filling factors, such as 19/13, which were predicted to occur due to correlations between nearly degenerate Landau levels more than two decades ago [2].

[1] Y Yoon Jang Chung, K. A. Villegas Rosale, K. W. Baldwin, P. T. Madathil, K. W. West, M. Shayegan, L. N. Pfeiffer, Nat. Mater. 20, 632–637 (2021).

[2] V. W. Scarola and J. K. Jain, Phys. Rev. B 64, 085313 (2001).