A mechanism of macroscopic rigid-body behavior through evanescent mode

It has been numerically found that the setup of Newton’s cradle can exhibit a rigid-body like behavior, that is, the target cluster starts to move collectively without emitting the outermost particle if the purely repulsive interaction between the neighbouring particles is very “soft” [KS, Phys. Rev. Lett. 104, 124302 (2010)]. We show theoretically that such an interaction leads to an evanescent mode within the cluster, which delivers the momentum within the cluster without any propagating oscillation.