Piezoresistivity as a Fingerprint of Ferroaxial Transitions

TL;DR

This paper demonstrates that off-diagonal piezoresistivity components can directly detect ferroaxial order parameters, introduces two new ferroaxial materials, and uses first-principles calculations to connect piezoconductivity with ferroaxial and octahedral rotation modes.

Contribution

It reveals a new method to measure ferroaxial order via piezoresistivity and identifies new ferroaxial materials using computational approaches.

Findings

Off-diagonal piezoresistivity components transform like ferroaxial moments.

Two new ferroaxial materials identified through database search.

First-principles calculations link piezoconductivity to ferroaxial order and octahedral rotations.

Abstract

Recent progress in the understanding of the collective behavior of electrons and ions have revealed new types of ferroic orders beyond ferroelectricity and ferromagnetism, such as the ferroaxial state. The latter retains only rotational symmetry around a single axis and reflection symmetry with respect to a single mirror plane, both of which are set by an emergent electric toroidal dipole moment. Due to this unusual symmetry-breaking pattern, it has been challenging to directly measure the ferroaxial order parameter, despite the increasing attention this state has drawn. Here, we show that off-diagonal components of the piezoresistivity tensor (i.e., the linear change in resistivity under strain) transform the same way as the ferroaxial moments, providing a direct probe of such order parameters. We identify two new proper ferroaxial materials through a materials database search, and use first-principles calculations to evaluate the piezoconductivity of the double-perovskite CaSnF$_6$, revealing its connection to ferroaxial order and to octahedral rotation modes.