Dual mechanisms for transient capacitance anomaly in improper ferroelectrics

TL;DR

This paper investigates transient negative capacitance in improper ferroelectric h-YbFeO3 films, revealing that inhomogeneous and homogeneous mechanisms dominate at different switching stages, with implications for ferroelectric device applications.

Contribution

It provides a combined experimental and phenomenological model analysis showing dual mechanisms behind transient negative capacitance in improper ferroelectrics.

Findings

Early-stage negative capacitance due to inhomogeneous switching involving domain wall motion.

Late-stage negative capacitance linked to thermodynamically unstable homogeneous switching.

Reconciliation of conflicting mechanisms in polarization switching.

Abstract

The recent discovery of transient negative capacitance has sparked an intense debate on the role of homogeneous and inhomogeneous mechanisms in polarizations switching. In this work, we report observation of transient negative capacitance in improper ferroelectric h-YbFeO3 films in a resistor-capacitor circuit, and a concaved shape of anomaly in the voltage wave form, in the early and late stage of the polarizations switching respectively. Using a phenomenological model, we show that the early-stage negative capacitance is likely due to the inhomogeneous switching involving nucleation and domain wall motion, while the anomaly at the late stage, which appears to be a reminiscent negative capacitance is the manifestation of the thermodynamically unstable part of the free-energy landscape in the homogeneous switching. The complex free-energy landscape in hexagonal ferrites may be the key to cause the abrupt change in polarization switching speed and the corresponding anomaly. These results reconcile the two seemingly conflicting mechanisms in the polarization switching and highlight their different roles at different stages. The unique energy-landscape in hexagonal ferrites that reveals the dual switching mechanism suggests the promising application potential in terms of negative capacitance.