Magnetic Susceptibility in Strongly Coupled Systems
  We study the magnetic susceptibility at large 't Hooft coupling by computing the correlation function of the magnetizations in the strongly coupled Maxwell theory in large-N limit with finite temperature and chemical potential, within the framework of the AdS/CFT correspondence. We show that in strong coupling limit the magnetic susceptibility is independent to the temperature and be universal, measured in the unit of magnetic permeability of the bulk space. A comparison with the weak coupling system, the Pauli paramagnetic susceptibility, is also discussed. 
M. J. Luo
hep-th cond-mat.str-el