Correlation Decoupling of Casimir Interaction in an Electrolyte Driven by External Electric Fields

It is well established that the long-range van der Waals or thermal Casimir interaction between two semi-infinite dielectrics separated by a distance H is screened by an intervening electrolyte. Here we show how this interaction is modified when an electric field of strength E is applied parallel to the dielectric boundaries, leading to a nonequilibrium steady state with a current. The presence of the field induces a long-range thermal repulsive interaction, scaling just like the thermal Casimir interaction between dielectrics without the intervening electrolyte, i.e., as 1/H³. At small E the effect is of order E², while at large fields it saturates to an E independent value. We explain the results in terms of a decoupling mechanism between the charge density fluctuations of cations and anions at large applied fields.