Coulomb drag at zero temperature

We show that the Coulomb drag effect exhibits saturation at small temperatures, when calculated to the third order in the interlayer interactions. The zero-temperature transresistance is of the order h/(e(2)g(3)), where g is the dimensionless sheet conductance. The effect is therefore the strongest in low mobility samples. This behavior should be contrasted with the conventional (second order) prediction that the transresistance scales as a certain power of temperature and is (almost) mobility independent. The result demonstrates that the zero-temperature drag is not an unambiguous signature of a strongly coupled state in double-layer systems.