Terahertz Induced Photoconductivity of 2D Electron System in HEMT at Low   Magnetic Field
  A few results of our study of two-dimensional electron system (2DES) in low magnetic fields in GaAs/GaAlAs heterostructures by cyclotron resonance (CR) and photoconductivity techniques are presented. We have first discovered "CR-vanishing effect"in 2DES as well-defined crevasse on CR line in low magnetic fields, when Hall resistance is not quantized. "CR-vanishing effect" indicates vanishing longitudinal resistance & conductivity in these magnetic fields. Observed "CR-vanishing effect" demonstrates new correlated state of electrons in 2DES. 
Andrey Chebotarev and Galina Chebotareva