Coulomb singularity effects in tunnelling spectroscopy of individual   impurities
  Non-equilibrium Coulomb effects in resonant tunnelling processes through deep impurity states are analyzed. It is shown that Coulomb vertex corrections to the tunnelling transfer amplitude lead to a power-law singularity in current- voltage characteristics 
P.I.Arseyev, N.S.Maslova, V.I.Panov and S.V.Savinov