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Competing quantum Hall phases in the second Landau level in the low-density limit

Pan, Wei P.; Serafin, A.; Xia, J.S.; Liang, Y.; Sullivan, N.S.; Baldwin, K.W.; West, K.W.; Pfeiffer, L.N.; Tsui, D.C.

In this Rapid Communication we present the results from two high-quality, low-density GaAs quantum wells. In sample A of electron density n = 5.0 × 1010 cm-2, anisotropic electronic transport behavior was observed at ν = 7/2 in the second Landau level. We believe that the anisotropy is due to the large Landau level mixing effect in this sample. In sample B of density 4.1 × 1010 cm-2, strong 8/3, 5/2, and 7/3 fractional quantum Hall states were observed. Furthermore, our energy gap data suggest that, similar to the 8/3 state, the 5/2 state may also be spin unpolarized in the low-density limit. The results from both samples show that the strong electron-electron interactions and a large Landau level mixing effect play an import role in the competing ground states in the second Landau level. © 2014 American Physical Society.