Stability of Reissner-Nordstr\"om black hole in de Sitter background   under charged scalar perturbation
  We find a new instability in the four-dimensional Reissner-Nordstrom-de Sitter black holes against charged scalar perturbations with vanishing angular momentum, $l=0$. We show that such an instability is caused by superradiance. The instability does not occur for an larger angular index, as explicitely proven for $l=1$. Our results are obtained from a numerical investigation of the time domain profiles of the perturbations. 
Zhiying Zhu, Shao-Jun Zhang, C. E. Pellicer, Bin Wang, Elcio Abdalla
hep-th gr-qc