Topological piezomagnetic effect in two-dimensional Dirac quadrupole altermagnets

TL;DR

This paper introduces 2D Dirac quadrupole altermagnets and reveals their topological piezomagnetic response, linking strain effects to the behavior of Dirac points in these novel materials.

Contribution

The study identifies a topological orbital piezomagnetic effect in 2D Dirac quadrupole altermagnets based on microscopic models, connecting strain response to topological electronic structures.

Findings

Topological piezomagnetic polarizability has a topological contribution.

Strain affects Dirac points, inducing a piezomagnetic response.

Proposed models include a spinless two-band and a Lieb lattice with Néel order.

Abstract

Altermagnets provide a natural platform for studying and exploiting piezomagnetism. In this paper, we introduce a class of insulating altermagnets in two dimensions (2D) referred to as Dirac quadrupole altermagnets, and show based on microscopic minimal models that the orbital piezomagnetic polarizability of such altermagnets has a topological contribution described by topological response theory. The essential low-energy electronic structure of Dirac quadrupole altermagnets can be understood from a gapless parent phase (i.e., the Dirac quadrupole semimetal), which has important implications for their response to external fields. Focusing on the strain-induced response, here we demonstrate that the topological piezomagnetic effect is a consequence of the way in which strain affects the Dirac points forming a quadrupole. We consider two microscopic models: a spinless two-band model describing a band inversion of $s$ and $d$ states, and a Lieb lattice model with collinear N\'eel order. The latter is a prototypical minimal model for altermagnetism in 2D and is realized in a number of recently proposed material compounds, which are discussed.