Flexoelectricity in two-dimensional materials

Matteo Springolo, Miquel Royo, Massimiliano Stengel

Published 2020-10-16Version 1

Flexoelectricity, the generation of a macroscopic polarization or voltage in response to strain gradients, is expected to be remarkably large in two-dimensional (2D) crystals. Here, building on recent developments in electronic-structure methods, we develop the theoretical tools to define and calculate flexoelectricity in 2D materials fully from first principles. In particular, we show that the voltage response to a flexural deformation can be calculated within a supercell geometry, corresponding to the surface unit cell of the flat configuration. By applying our methodology to graphene, silicene, phosphorene, BN and transition-metal dichalcogenide monolayers, we demonstrate that two distinct contributions exist, respectively of purely electronic and lattice-mediated nature. Within the former, we identify a key geometric term, originating from the rigid deformation of the unperturbed electronic density.