Polarization at the Nanoscale

TL;DR

This paper develops a real-space method to analyze polarization in nanoscale systems, revealing how surface effects influence polarization and piezoelectricity in materials like semiconductors and BaTiO3.

Contribution

It introduces a novel real-space approach for total polarization that captures nanoscale surface effects and demonstrates its application to specific materials.

Findings

Surface passivation quenches piezoelectricity at the nanoscale

The approach agrees with Berry phase calculations for bulk polarization

Surface phenomena significantly affect nanoscale polarization behavior

Abstract

Modern polarization theory yields surface bound charge associated with spontaneous polarization of bulk. However, understanding polarization in nano systems also requires a proper treatment of charge transfer between surface dangling bonds. Here, we develop a real-space approach for total polarization and apply it to wurtzite semiconductors and BaTiO3 perovskite. First-principles calculations utilizing this approach not only yield spontaneous bulk polarization in agreement with Berry phase calculations, but also uncover phenomena specific to nano systems. As an example, we show surface passivation leads to a complete quenching of the piezoelectric effect, which reemerges only at larger length scale and/or spontaneous polarization.