Absolute negative conductivity and zero-resistance states in two   dimensional electron systems: A plausible scenario
  We present a model which provides a plausible explanation of the effect of zero-resistance and zero-conductance states in two-dimensional electron systems subjected to a magnetic field and irradiated with microwaves observed in a number of experiments and of the effect main features. The model is based on the concept of absolute negative conductivity associated with photon-assisted scattering of electrons on impurities. It is shown that the main features of the effect can be attributed to the interplay of different electron scattering mechanisms. 
V.Ryzhii, A.Chaplik, and R.Suris