Unified definition of ferroelectricity

TL;DR

This paper proposes a unified definition of ferroelectricity based on switchable polarization differences, enabling systematic identification of both conventional and quantum ferroelectrics through high-throughput screening.

Contribution

It introduces a new unified polarization-based definition of ferroelectricity and demonstrates its application in discovering novel quantum ferroelectrics.

Findings

Identified a new quantum ferroelectric with polarization from arbitrary ionic displacements.

Discovered materials like Ba3I6 and Cs2PdC2 with low switching barriers.

Reconciled conventional and quantum ferroelectrics under a unified framework.

Abstract

Recent theoretical and experimental advances in quantum ferroelectrics suggest that ferroelectricity can also emerge in non-polar space group, highlighting the limitations of conventional polar space group criteria in identifying ferroelectric materials. Here, we introduce a unified definition based on switchable polarization differences between energetically equivalent states, which naturally encompasses conventional and quantum ferroelectrics. Guided by this principle, we implement a high-throughput screening strategy that systematically identifies both conventional and quantum ferroelectrics among experimentally synthesized materials. In particular, we identify a new type of quantum ferroelectric in which the quantized polarization arises from arbitrary ionic displacements, in contrast to previous quantum ferroelectrics (including both fractional and integer quantum ferroelectrics) where quantized polarization results from fractional or integer ionic displacements. Notably, we find that materials such as Ba3I6 and Cs2PdC2 exhibit low switching barriers and robust insulating behavior, highlighting their experimental viability. Our results reconcile conventional and quantum ferroelectrics, expand the accessible materials landscape, and provide a practical roadmap for discovering next-generation ferroelectrics with advanced switchable functionalities.