Tuning of altermagnetism by strain

TL;DR

This paper investigates how strain influences altermagnetism, identifying symmetry-allowed responses, mechanisms, and first-principles calculations, and explores the impact of strain on triplet superconductivity in altermagnets.

Contribution

It provides a comprehensive symmetry-based classification of strain-induced effects in altermagnets and explores their implications for superconductivity and magnetic responses.

Findings

Strain induces piezomagnetic effects via Dzyaloshinskii-Moriya interaction.

Two mechanisms for strain effects: band-filling and exchange-driven.

Strain can alter the nature of triplet superconductivity in altermagnets.

Abstract

For all collinear altermagnets, we sort out piezomagnetic free-energy invariants allowed in the nonrelativistic limit and relativistic piezomagnetic invariants bilinear in the N\'eel vector $\mathbf{L}$ and magnetization $\mathbf{M}$, which include strain-induced Dzyaloshinskii-Moriya interaction. The symmetry-allowed responses are fully determined by the nonrelativistic spin Laue group. In the nonrelativistic limit, two distinct mechanisms are discussed: the band-filling mechanism, which exists in metals and is illustrated using the simple two-dimensional Lieb lattice model, and the temperature-dependent exchange-driven mechanism, which is illustrated using first-principles calculations for transition-metal fluorides. The leading second-order nonrelativistic term in the strain-induced magnetization is also obtained for CrSb. Piezomagnetism due to the strain-induced Dzyaloshinskii-Moriya interaction is calculated from first principles for transition-metal fluorides, MnTe, and CrSb. Finally, we discuss triplet superconducting correlations supported by altermagnets and protected by inversion rather than time-reversal symmetry. We apply the nonrelativistic classification of Cooper pairs to describe the interplay between strain and superconductivity in the two-dimensional Lieb lattice and in bulk rutile structures. We show that triplet superconductivity is, on average, unitary in an unstrained altermagnet, but becomes non-unitary under piezomagnetically active strain.