On the zero-resistance states generated by radiation in GaAs/AlGaAs
  The applied radiation excites "holes". The condensed composite (c)-bosons formed in the excited channel create a superconducting state with an energy gap. The supercondensate suppresses the non-condensed c-bosons at low temperatures, but it cannot suppress the c-fermions in the base channel, and the small normal current accompanied by the Hall field yields a B-linear Hall resistivity. 
S. Fujita and K. Ito