The effect of Coulomb correlations on non-equilibrium charge   redistribution tuned by the tunneling current
  It was shown that tunneling current flowing through a system with Coulomb correlations leads to charge redistribution between the different localized states. Simple model consisting of two electron levels have been analyzed by means of Heisenberg motion equations taking into account all order correlations of electron filling numbers in localized states exactly. We consider various relations between Coulomb interaction and localized electron energies. Sudden jumps of electron density at each level in a certain range of applied bias have been found. We found that for some parameter range inverse occupation in the two-level system appeared due to Coulomb correlations. It was shown also that Coulomb correlations lead to appearance of negative tunneling conductivity at certain relation between the values of tunneling rates from the two electronic levels. 
P.I. Arseyev, N.S. Maslova, V.N. Mantsevich
cond-mat.other