Nature of coupling mechanisms between pancake vortices in neighboring superconducting layers

Layered type-II superconductors (say, Bi₂{Sr}₂CaCu₂{O}₈$ and superconductor/insulator superlattices) possess fascinating mixed states. A flux line at an angle with the superconducting layers may be cut into a series of pancake vortices. In the existing literature, the interactions between these vortices have been attributed to a combination of magnetic and Josephson effects. Both these effects lead to an attraction between pancake vortices in neighboring superconducting layers. We show that there exists a third mechanism of interaction, namely the indirect effect of the Coulomb interaction, which leads to a repulsion between such vortices. The relative strength of this coupling is estimated. We consider the competition between different mechanisms and solve the effective total Hamiltonian asymptotically for small in-plane separation between neighboring pancake vortices. The third coupling mechanism is an observable consequence of vacuum fluctuations.