Multipolar Piezoelectricity and Anisotropic Surface Transport in Alterelectrics

TL;DR

This paper introduces alterelectrics, a new class of materials with quadrupolar piezoelectricity and hyperbolic dispersion, demonstrating their potential for anisotropic surface transport similar to altermagnets.

Contribution

The work proposes alterelectrics as an alternative to altermagnets, showing their quadrupolar piezoelectricity, hyperbolic dispersion, and surface-dependent anisotropic transport through models and first-principles calculations.

Findings

Alterelectrics exhibit quadrupolar piezoelectricity.

They demonstrate hyperbolic wave dispersion.

Surface modes enable anisotropic electronic transport.

Abstract

Altermagnets are an emergent class of materials combining features of ferro- and antiferro-magnetic materials. They have spin-separated bands normally associated with ferromagnets, but a vanishing net magnetization. Moreover the symmetries giving rise to $d$-wave altermagnetism can provide them with a particular anisotropic, quadrupolar (i.e. with equal and opposite values when strained in perpendicular directions) piezomagnetism. Observing that the same symmetries provide a natural place to look for hyberbolic wave dispersion, this raises the question which properties are intrinsically linked to magnetism and which are determined by the symmetry. Here, we disentangle these concepts by introducing an alternative to altermagnets, based on electric polarization. These alterelectrics display quadrupolar piezoelectricity and a hyperbolic dispersion, which we demonstrate conceptually within a simplified model as well as a first-principles material realization. We furthermore establish that a counterpart of the spin-separated bands is formed by surface modes which allow for surface dependent anisotropic electronic transport analogous to the spintronic applications proposed for altermagnets.