Fluctuations of a holographic quantum Hall fluid
  We analyze the neutral spectrum of the holographic quantum Hall fluid described by the D2-D8' model. As expected for a quantum Hall state, we find the system to be stable and gapped and that, at least over much of the parameter space, the lowest excitation mode is a magneto-roton. In addition, we find magneto-rotons in higher modes as well. We show that these magneto-rotons are direct consequences of level crossings between vector and scalar modes. 
Niko Jokela, Matti Jarvinen, and Matthew Lippert
hep-th cond-mat.str-el