The effective action of (2+1)-dimensional QED: the effect of finite   fermion density
  The effective action of (2+1)-dimensional QED with finite fermion density is calculated in a uniform electromagnetic field. It is shown that the integer quantum Hall effect and de Haas-van Alphen like phenomena in condensed matter physics are derived directly from the effective action. 
Dae Kwan Kim (Seoul National University) and Kwang-Sup Soh (Seoul   National University)