Microwave resonance of the reentrant insulating quantum Hall phases in   the 1st excited Landau Level
  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 $\nu=2.58$ and weaker frequency dependence is seen at $\nu=2.42$ and 2.28. These measurements are consistent with the formation of a bubble phase crystal centered around these $\nu$ at very low temperatures. 
R. M. Lewis, Yong P. Chen, L. W. Engel, D. C. Tsui, L. N. Pfeiffer,   and K. W. West