Spontaneous altermagnetism in multi-orbital correlated electron systems

TL;DR

This paper predicts a new class of spontaneous altermagnets in multi-orbital correlated systems, revealing novel magnetic and magnonic phenomena with potential spintronics applications.

Contribution

It introduces a microscopic mechanism for spontaneous altermagnetism in three-orbital systems, circumventing traditional rules and uncovering chiral magnons and hybrid modes.

Findings

Identification of a spontaneous altermagnetic Mott insulator.

Discovery of chirally split magnons with measurable spin conductivities.

Prediction of a hybrid magnon-orbiton mode induced by magnetic fields.

Abstract

Altermagnets have attracted considerable attention in recent years owing to their potential technological applications in spintronics and magnonics. Recently, a new class of spontaneous altermagnets has been theoretically predicted in a correlated two orbital model, driven by the coexistence of antiferromagnetic spin and staggered orbital ordering, thus broadening the scope of altermagnetic phenomena to systems with strong correlations. It has been noted, however, that the required spin and orbital order violates the well-established Goodenough-Kanamori (GK) rules, which underlie much of our understanding of magnetism in complex systems. Here we show that materials with three active orbitals may offer a more realistic route to this exotic state. Specifically, we consider a two-dimensional system with $t_{2g}^{2}$ electrons and identify a novel microscopic mechanism that allows the formation of a spontaneous altermagnetic Mott insulator. We explain how the GK rules are circumvented and provide the stability criteria by employing unbiased mean-field and density matrix renormalization group calculations. In addition, for the first time, we uncover the presence and microscopic origin of chirally split magnons in these spontaneous altermagnets, with experimentally measurable spin conductivities. Finally, we predict that the application of a small in-plane magnetic field induces, in the presence of weak atomic spin-orbit coupling, an as-yet unreported hybrid chiral magnon-orbiton mode with a non-zero orbital polarization giving rise to finite longitudinal and transverse orbital conductivities under a thermal gradient.