Coherent tunnelling through two quantum dots with Coulomb interaction
  The coherent conductance and current is calculated through two quantum dots using the Hubbard model for a single level per spin. The occurrence of negative differential conductance is demonstrated. The Ohmic conductance is calculated for dots with equally spaced levels. Transport is determined by matching energy levels, even when they do not occur at the charge degeneracy points. 
P. Pals and A.MacKinnon (The Blackett Laboratory, Imperial College,   London, United Kingdom)