Direct and converse flexoelectricity in two-dimensional materials

TL;DR

This paper develops a first-principles method to calculate the flexoelectric response of 2D materials, revealing electronic and lattice contributions, and connects theory with experimental measurements.

Contribution

It introduces a novel first-principles approach to quantify flexoelectricity in 2D materials, identifying electronic and lattice effects and proposing a continuum model.

Findings

Identified electronic and lattice contributions to flexoelectricity in 2D materials.

Calculated flexoelectric response for graphene, silicene, phosphorene, BN, and TMD monolayers.

Connected theoretical predictions with experimental measurements of the converse flexoelectric effect.

Abstract

Building on recent developments in electronic-structure methods, we define and calculate the flexoelectric response of two-dimensional (2D) materials fully from first principles. In particular, we show that the open-circuit voltage response to a flexural deformation is a fundamental linear-response property of the crystal that can be calculated within the primitive unit cell of the flat configuration. Applications to graphene, silicene, phosphorene, BN and transition-metal dichalcogenide monolayers reveal that two distinct contributions exist, respectively of purely electronic and lattice-mediated nature. Within the former, we identify a key $metric$ term, consisting in the quadrupolar moment of the unperturbed charge density. We propose a simple continuum model to connect our findings with the available experimental measurements of the converse flexoelectric effect.