Electronic flexoelectricity in low-dimensional systems

Symmetry breaking at surfaces and interfaces and the capability to support large strain gradients in nanoscale systems enable unusual forms of electromechanical coupling. Here, we introduce the concept of electronic flexoelectricity, a phenomenon that is manifested when the mechanical deformation of nonpolar quantum systems results in the emergence of net dipole moments and hence linear electromechanical coupling proportional to local curvature. The concept is illustrated in carbon systems, including polyacetylene and nanographitic ribbons. Using density functional theory calculations for systems made of up to 400 atoms, we determine the flexoelectric coefficients to be of the order of $\ensuremath{\sim}0.1e$, in agreement with the prediction of linear theory. The implications of electronic flexoelectricity on electromechanical device applications and physics of carbon-based materials are discussed.