  Coulomb drag is a transport phenomenon whereby long-range Coulomb interaction
between charge carriers in two closely spaced but electrically isolated
conductors induces a voltage (or, in a closed circuit, a current) in one of the
conductors when an electrical current is passed through the other. The
magnitude of the effect depends on the exact nature of the charge carriers and
microscopic, many-body structure of the electronic systems in the two
conductors. Drag measurements have become part of the standard toolbox in
condensed matter physics that can be used to study fundamental properties of
diverse physical systems including semiconductor heterostructures, graphene,
quantum wires, quantum dots, and optical cavities.
