GROUND-STATE AT LOW LANDAU-LEVEL FILLING FACTORS IN 2-DIMENSIONAL SYSTEMS OF GAAS ALGAAS HETEROSTRUCTURES IN STRONG MAGNETIC-FIELDS/

Integer and fractional quantum Hall effects are interesting phenomena in two-dimensional electron systems (2DES) in strong magnetic fields. In this paper, breakdown of the integer quantum Hall effect (IQHE) at odd integer filling factors at 100 mK and temperature dependence of th e fractional quantum Hall effect (FQHE) around the filling facor nu=1/ 2 at temperatures between 100 mK and 1000 mK in magnetic fields up to 25 T are measured for the 2DES in two AlGaAs/GaAs heterostructures. Th e results in the IQHE measurements are compared with results at the ev en filling factors and derive the effective g-factor of about 10 in th is system. The results in the FQHE measurements at nu=1/2 shows a loga rithmic temperature dependence of the conductivity which is expected i n a weakly localized Fermion system in zero magnetic fields.