Millimeter wave and DC investigations of spin effects in the 2DES of AlGaAs/GaAs

The spin properties of the 2DES in AlGaAs/GaAs heterostructures are studied via the electron spin resonance (ESR) of conduction electrons and via the temperature dependence of the DC-σxx(B) conductivity component. The ESR is investigated at integer (ν=1) and fractional filling factors (ν<1) via the change ΔRxx of the magnetoresistance in high- and low-mobility samples. The DC-σxx(B) peaks in the integer quantum Hall effect regime show scaling behaviour. The peak widths obey power laws with exponents of about 0.4 (strong spin splitting) and 0.2 (no spin splitting, one critical energy in the Landau level centre). By assuming two critical energies in the latter case we obtain exponents close to 0.4.