Hysteretic behavior and evidence for domain formation in a double-layer   quantum Hall system at total filling factor 2
  We report anomalous behavior in a double-layer two dimensional hole gas (2DHG) at even integer filling factors which includes hysteresis in the longitudinal and Hall resistances and a very weak temperature dependence of the resistance minima. All anomalies disappear and the conventional quantum Hall effect behavior recovers when a thin metal film is placed on top of the 2DHG. The behavior is attributed to presence of the theoretically predicted magnetic ordering at even integer filling factors which causes the formation of macroscopic spin-charge domains. 
J.G.S. Lok, A.K. Geim, B. Tieke, J.C. Maan (High Field Magnet   Laboratory, Research Institute for Materials, University of ...