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Microwave resonance of the reentrant insulating quantum Hall phases in the 1st excited Landau Level

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 Added by Rupert M. Lewis
 Publication date 2004
  fields Physics
and research's language is English




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We present measurements of the real diagonal microwave conductivity of the reentrant insulating quantum Hall phases in the first excited Landau level at temperatures below 50 mK. A resonance is detected around filling factor $ u=2.58$ and weaker frequency dependence is seen at $ u=2.42$ and 2.28. These measurements are consistent with the formation of a bubble phase crystal centered around these $ u$ at very low temperatures.



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We present in this Letter the results from two high quality, low density GaAs quantum wells. In sample A of electron density n=5.0x10^10 cm^-2, anisotropic electronic transport behavior was observed at u=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 4.1x10^10 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.
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