Transport of Indirect Excitons in a Potential Energy Gradient
  We realized a potential energy gradient - a ramp - for indirect excitons using a shaped electrode at constant voltage. We studied transport of indirect excitons along the ramp and observed that the exciton transport distance increases with increasing density and temperature. 
J. R. Leonard, M. Remeika, M. K. Chu, Y. Y. Kuznetsova, A. A. High, L.   V. Butov, J. Wilkes, M. Hanson, and A. C. Gossard
cond-mat.mes-hall