Evidence for a New Dissipationless Regime in 2D Electronic Transport
  In an ultra-clean 2D electron system (2DES) subjected to crossed millimeterwave (30--150 GHz) and weak (B < 2 kG) magnetic fields, a series of apparently dissipationless states emerges as the system is detuned from cyclotron resonances. Such states are characterized by an exponentially vanishing low-temperature longitudinal resistance and a classical Hall resistance. The activation energies associated with such states exceeds the Landau level spacing by an order of magnitude. Our findings are likely indicative of a collective ground state previously unknown for 2DES. 
M. A. Zudov, R. R. Du, L. N. Pfeiffer, and K. W. West