Interfacial Non-reciprocal Interactions

Water polarization near an interface defies our understanding of electrostatics and leads to non-equivalent and directional interactions. We have found that the attraction between two oppositely charged ions near a graphene surface is enhanced in the surface normal direction while no major changes are found in the surface parallel direction. This attraction is further enhanced by decreasing the confinement distance and the interaction becomes repulsive when one ion is intercalated into the graphene layers. Surprisingly, upon exchange of the ions’ positions the interaction is not equivalent as in the bulk, namely, by interchanging the ions' position there is an energy difference of about 5kBT. These non-equivalent and directional properties are referred to as non-reciprocal interactions and cannot be explain by current water permittivity models in confinement.