Enhanced stark effect in Dirac materials.

The Stark effect in confined geometries is sensitive to boundary conditions. The vanishing wave function required on the boundary of nanostructures described by the infinite-barrier Schrödinger equation means that such states are only weakly polarizable. In contrast, materials described by the Dirac equation are characterized by much less restrictive boundary conditions. Focusing on honeycomb-lattice armchair nanoribbons, we demonstrate an enhancement by more than an order of magnitude. This result follows from an exact Dirac polarizability valid for arbitrary mass, momentum and ribbon width. Moreover, an exact expression for the frequency-dependent dynamic polarizability has been derived. Our analytic Dirac results have been validated by comparison to numerical results from atomistic models.