Understanding the Optical Dielectric Constant of Nanoconfined Ice Capacitors

The relative out of plane dielectric constant of nano confined water in graphene capacitors was shown to be as low as 2.1 for capacitor thickness below 1 nm by Fumagalli et al. (Science 360, 2018). It is surprising because such a low measured value is even lower than the high frequency dielectric constant of ice. In this work, we apply the concept of two dimensional transverse polarizability to relate capacitance measurements to the dielectric constant of a nanoconfined ice capacitor. Doing this, we will show that the electronic response is strongly dependent on the local order of water molecules at the interfaces. Our results highlight the importance of considering electronic effects in computing dielectric properties of nanoconfined systems.