Comment on "Spin-Gradient-Driven Light Amplification in a Quantum   Plasma"
  A comment on the Letter by S. Braun, F. A. Asenjo and S. M. Mahajan, Phys. Rev. Lett., 109, 175003 (2012). We show that recent arguments for light amplification driven by inhomogeneous quantum spin fields in low temperature electron plasmas in metals are invalid. In essence, a neglect of Pauli `blocking' led the authors to over-estimate the effects of intrinsic spin. 
Govind S. Krishnaswami, Rajaram Nityananda, Abhijit Sen,   Anantanarayanan Thyagaraja
physics.plasm-ph cond-mat.other physics.flu-dyn