The relationship of electron Fermi energy with strong magnetic fields
  In order to depict the quantization of Landau levels, we introduce Dirac $\delta$ function, and gain a concise expression for the electron Fermi energy, $E_{F}(e) \propto B^{1/4}$. The high soft X-ray luminosities of magnetars may be naturally explained by our theory. 
Qiu He Peng, Zhi Fu Gao, and Na Wang
astro-ph.HE cond-mat.mes-hall