Hydrodynamics of electron-hole Coulomb drag

A remarkable response of a three-component hydrodynamic plasma consisting of electrons, light holes, and heavy holes to an external electric field has been discovered in a quantum well structure where the field causes counterflows of light and heavy holes: Heavy holes propagate in the direction of the electric field, while light holes move in the direction opposite to the electric field, in the same direction as the electrons. The observed effect is due to the different scattering efficiencies of electrons by light and heavy holes, which causes the Coulomb drag of light holes by electrons, while the drift in the electric field is responsible for the propagation of heavy holes. As a consequence of the Coulomb electron-hole drag, negative conductivity of light holes is observed.