Coulomb Drag in Systems with Tunneling Bridges

We study the Coulomb drag effect in double layer electronic systems with local tunneling links. The possibility of tunneling between the layers leads to a pronounced exchange contribution to the transconductance, which is negative and nonvanishing at zero temperature. The diffusive motion of the electrons inside each layer in interplay with the electron-electron interaction causes a distinct singular temperature dependence of the transconductance at low temperatures.