New resistance maxima of the 2DEG at fractional filling factors

Magneto-resistance measurements in narrow single quantum wells show very sh arp (width approximate to 0.2 T) maxima at fractional filling factors betwe en 1 and 1/2. The peak values of the new maxima exceed the resistance value s in the surrounding magnetic held region by a factor oi: up to 3. The form ation of the maxims is hysteretic and takes place on a long time scale. Thi s points towards a close relation with the nuclear spins. Those new maxima will be discussed in the framework of domains having two different spin gro und states. (C) 1998 Published by Elsevier Science B.V. All rights reserved .