It was recalled that, in electromigration experiments on metallic wires, a flux of atoms could lead to movement of the center of mass of the wire. It was therefore natural to assume that the flow of current produced a net force on the whole wire. It was pointed out, on the basis of known momentum-balance arguments, that the net force on a metallic wire - due to passing a steady-state current - was zero. This was because, in addition to electromigration driving forces acting on scattering centers, there were counterbalancing forces which acted on the rest of the system. Drift of the center of mass in electromigration experiments were inevitable because the substrate kept fixed the crystal lattice of the wire, while permitting defect diffusion in the bulk of the wire. This drift was not evidence for a net force on the wire.

Counterbalancing Forces in Electromigration. J.Hoekstra, A.P.Sutton, T.N.Todorov: Journal of Physics - Condensed Matter, 2002, 14[6], L137-40

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