Coulomb repulsion between electrons in quantum dots is supposed to suppress current. Add more repulsion, get less flow. This is the standard result for linear quantum dot arrays, where interaction-induced energy shifts block the transport channel.
Ren and colleagues studied a triangular triple quantum dot and found the opposite. Increasing the Coulomb interaction parameter enhances the stationary current. The mechanism: in the triangular topology, Coulomb-induced energy shifts open new interference pathways that constructively combine with the chiral circulation unique to the three-site geometry. The same Coulomb repulsion that blocks in a line accelerates in a triangle.
In a different system, Gao and colleagues derived scaling laws for entropic separation of tether-mediated nanofilament bundles. The entropic force between filaments — which ordinarily pushes them apart — reverses sign when a single dimensionless parameter crosses a threshold. That parameter is the ratio of excluded-volume radius to tether length. Above the threshold, entropy drives disaggregation as expected. Below it, the same entropic force produces attractive metastable states, pulling the filaments together.
The structural parallel: in both cases, the sign of the effect is a property of the geometry, not the interaction. The same Coulomb repulsion suppresses or enhances depending on the dot topology. The same entropic force repels or attracts depending on the tether geometry. The interaction itself doesn't change — its character doesn't flip, its magnitude doesn't reverse. What changes is the topological context in which it operates. This is not the claim that geometry matters (obvious) or that topology modulates magnitude (well-known). It is the sharper claim that topology determines the sign. Positive becomes negative. Obstruction becomes aid. The qualitative character of the effect — not just how much, but whether it helps or hinders — is controlled by the shape of the arena. The implications run further than quantum dots and nanofilaments. If the sign of an interaction depends on topology, then measuring the interaction in one geometry and extrapolating to another is not just imprecise — it is wrong in direction. The physicist who characterizes Coulomb effects in a linear array and applies the result to a triangular one does not get a less accurate answer. She gets a wrong-sign answer. The error is not quantitative but qualitative. This is the deep reason topology matters in physics: not because it adds corrections to the interaction, but because it can invert the interaction's meaning.