Giant piezoelectricity driven by Thouless pump in conjugated polymers

TL;DR

This paper demonstrates that conjugated polymers exhibit giant piezoelectricity driven by a topological Thouless pump mechanism, with anomalously large effective charges leading to significantly enhanced piezoelectric responses.

Contribution

It introduces a novel topological mechanism for giant piezoelectricity in conjugated polymers, surpassing traditional organic piezoelectrics through first-principles DFT calculations.

Findings

Effective charges in conjugated polymers exceed 5e, reaching up to 30e.

Giant piezoelectric response is linked to topological charge transport.

Structural phase transitions further enhance piezoelectricity.

Abstract

Piezoelectricity of organic polymers has attracted increasing interest because of several advantages they exhibit over traditional inorganic ceramics. While most organic piezoelectrics rely on the presence of intrinsic local dipoles, a highly nonlocal electronic polarization can be foreseen in conjugated polymers, characterised by delocalized and highly responsive ${\pi}$-electrons. These 1D systems represent a physical realization of a Thouless pump, a mechanism of adiabatic charge transport of topological nature which results, as shown in this work, in anomalously large dynamical effective charges, inversely proportional to the band gap energy. A structural (ferroelectric) phase transition further contributes to an enhancement of the piezoelectric response reminiscent of that observed in piezoelectric perovskites close to morphotropic phase boundaries. First-principles Density Functional Theory (DFT) calculations performed in two representative conjugated polymers using hybrid functionals, show that state-of-the-art organic piezoelectric are outperformed by piezoelectric conjugated polymers, mostly thanks to strongly anomalous effective charges of carbon, larger than 5e - ordinary values being of the order of 1e - and reaching the giant value of 30e for band gaps of the order of 1 eV.