  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.
