Sign-reversal of drag in bilayer systems with in-plane periodic   potential modulation
  We develop a theory for describing frictional drag in bilayer systems with in-plane periodic potential modulations, and use it to investigate the drag between bilayer systems in which one of the layers is modulated in one direction. At low temperatures, as the density of carriers in the modulated layer is changed, we show that the transresistivity component in the direction of modulation can change its sign. We also give a physical explanation for this behavior. 
Audrius Alkauskas, Karsten Flensberg, Ben Yu-Kuang Hu, and Antti-Pekka   Jauho