Collective Excitations in Altermagnets and Antialtermagnets

I will review collective excitations in altermagnets and antialtermagnets. First, I will show how altermagnetism can emerge from orbital ordering [1]. Second, I will discuss the newly predicted spin demon mode in a d-wave altermagnet [2]. Third, I will demonstrate that magnons in altermagnets—such as hematite [3]—are unstable quasiparticles, as spin-split magnon bands enable spontaneous decay even at zero temperature [4]. I will then address how magnon–phonon coupling gives rise to an acoustic spin-splitter effect [5] and a d-wave phonon angular-momentum texture [6]. If time permits, I will also show that magnons in antialtermagnets display odd-parity spin splitting and that antiferromagnetic surfaces can inherit altermagnetic symmetries.